Although there have been marked fluctuations in the long-term trend, the rates of almost all types of interpersonal physical violence have decreased since the late middle ages.1 In medieval England the homicide rate was "... roughly twenty times those of modern Britain and up to double those ... in the contemporary United States."2 By the 1870s in the United States, judges no longer recognized the common-law right of husbands to use corporal punishment on wives. Even though wife beating remains a problem, the rate has continued to decline, along with the rate of physical abuse of children by their parents3,4 and homicides of wives by their husbands.5 An important exception to ending legal violence by citizens is spanking and other corporal punishment by parents, such as slapping a child's hand. In Canada and the United States corporal punishment of children by their parents is exempt from prosecution under the criminal code. The research by Harriet L. MacMillan and colleagues6 (page 805) adds to the mounting evidence that the time has come to end that exception. They studied a large community sample of Ontario residents and found that adults who remembered being slapped or spanked as children were twice as likely to report current alcohol abuse or dependence or to have externalizing problems (e.g., illicit drug abuse or dependence, antisocial behaviour) compared with adults who did not report being slapped or spanked as children. The study by MacMillan and colleagues and 5 recent longitudinal studies7-11 provide much more definitive evidence than existed even 3 years ago on the potential benefits of not spanking, including decreased lifetime risk of mental health problems and enhanced cognitive ability. Despite the strong evidence that spanking may be harmful, it may be difficult to stop the practice. A study in Ohio showed that 70% of 800 family physicians and 59% of 400 pediatricians supported spanking.12 In 1968, 94% of Americans, and perhaps also of Canadians, believed that spanking was sometimes necessary.13 Since then, national surveys in the United States have shown dramatic decreases,13 but a majority still think spanking is necessary. Actual spanking has also declined, although not to the same extent as people's attitudes have changed toward it. US national surveys of parents in 1975, 1985 and 1995 found little change in the proportion who reported hitting their toddlers (from 97% in 1975 to 94% in 1995).14 There was a greater decrease in the proportion who reported hitting their adolescent children; for example, among children aged 13 the proportion decreased from 55% in 1975 to 43% in 1995.14 The inconsistency between attitudes and prevalence rates is typical of the process of social change. Sweden and 8 other countries now ban spanking. Consistent with the humane principles underlying the Swedish ban, there are no provisions for criminal penalties, only for public education and for helping parents who are having trouble maintaining discipline. Fears that children would be "running wild" have proven to be unfounded.15 A Canadian advocacy group, Justice for Children, is challenging the constitutionality of section 43 of the Criminal Code, which exempts parents who spank their children from prosecution for assault. The accumulating evidence that spanking is harmful is too recent to explain the shift away from spanking in the last decade. Rather, this shift results from fundamental changes in society, starting with simple but basic trends such as the increasing levels of education. It is also reflects the long-term reduction of interpersonal violence and the extension of full human rights to those who previously did not have them (e.g., women). Another fundamental change is the emergence of a post-industrial economy and, with it, less need for people with the traits taught by spanking, such as unquestioned obedience. There is now less need for unskilled manual workers whose market value is primarily a willingness to do as they are told. Employers are seeking workers who can think for themselves, reason and negotiate. These abilities are modeled by alternative modes of discipline, not by spanking.16 Many unanswered questions remain. Is there a critical threshold for spanking that is safe if not exceeded (as argued by defenders of spanking), or is it a "dose-response"? Assuming that physicians are to advise against spanking, should they communicate an unambiguous "no-spanking" message in waiting-room posters and in consultations? I believe so, but most parent-educators do not; however, neither view is based on empirical data. What alternatives for discipline will be used when parents stop spanking? Many fear that parents will replace physical attacks with verbal attacks or that they will give up and abandon rules and standards. Although some parents will take those routes, in my opinion ending spanking will in general have the opposite result. It will sensitize parents to the vulnerability of children and result in fewer verbal attacks and greater rather than less attention to the child's behaviour. However, there is no scientific evidence for either view. Ending spanking is a mode of primary prevention to which physicians can make an important contribution. This will not be easy because most physicians, like most patients, believe that spanking is sometimes necessary. Consequently, medical societies and medical schools need to inform physicians about the evidence of serious lifetime side effects of being spanked as a child. However, the fact that the evidence, although strong, is not truly conclusive raises the question of whether advising parents not to spank is ethical and responsible. There are circumstances when it is. An example is research suggesting, even though not conclusively, that a certain drug has serious side effects. Advice based on that nondefinitive evidence would be appropriate if there is an equally effective drug that does not have those side effects. In the case of spanking, there is definitive experimental evidence that noncorporal disciplinary strategies are as effective in the immediate situation17,18 and longitudinal evidence of greater effectiveness in the long run.10 Thus, when parents avoid corporal punishment they are not giving up a necessary mode of discipline. Although the evidence suggests that ending spanking will reduce the prevalence of mental health problems and of violence and other crime, it will not eradicate these ancient problems. Moreover, every aspect of society, including the most salutary, poses problems for some people. Conversely, culturally approved practices that are harmful to most may also benefit many. This does not mean that it is impossible to identify what Edgerton calls "sick" aspects of society that, even though culturally valued, harm large numbers.19 The study by MacMillan and colleagues is part of a growing body of evidence that violent child-rearing under the euphemism of spanking is such an aspect. References Straus MA. Beating the devil out of them: corporal punishment in American families. San Francisco: Jossey-Bass/Lexington Books; 1994. Lane R. Murder in America: a history. Columbus: Ohio State University Press; 1997. p. 311. Straus MA, Gelles RJ. Societal change and change in family violence from 1975 to 1985 as revealed by two national surveys. J Marriage Family 1986;48:465-79. Straus MA. Trends in cultural norms and rates of partner violence: an update to 1992. In: Stith S, Straus MA, editors. Understanding partner violence: prevalence, causes, consequences, and solutions. Minneapolis: National Council on Family Relations; 1995. p. 30-3. Rosenfeld R. Changing relationships between men and women: a note on the decline in intimate partner homicide. Homicide Stud 1997;1:72-83. MacMillan HL, Boyle MH, Wong MYY, Duku EK, Fleming JE, Walsh CA. Slapping and spanking in childhood and its association with lifetime prevalence of psychiatric disorders in a general population sample. CMAJ 1999;161(7):805-9.[Abstract/Free Full Text] Brezina T. Teenage violence toward parents as an adaptation to family strain: evidence from a national survey of male adolescents. Youth Soc 1999;30:416-44. Gunnoe ML, Mariner CL. Toward a developmental-contextual model of the effects of parental spanking on children's aggression. Arch Pediatr Adolesc Med 1997;151:768-75.[Abstract] Simons RL, Lin KH, Gordon LC. Socialization in the family of origin and male dating violence: a prospective study. J Marriage Family 1998;60:467-78. Straus MA, Sugarman DB, Giles-Sims J. Spanking by parents and subsequent antisocial behavior of children. Arch Pediatr Adolesc Med 1997;151:761-7.[Abstract] Straus MA, Paschall MJ. Corporal punishment by mothers and children's cognitive development: a longitudinal study of two age cohorts. Proceedings of the 6th International Family Violence Research Conference; 1999 July 27; Durham, New Hampshire. Durham (NH): Family Research Laboratory, University of New Hampshire; 1999. McCormick KF. Attitudes of primary care physicians toward corporal punishment. JAMA 1992;267:3161-4.[Abstract] Straus MA, Mathur AK. Social change and change in approval of corporal punishment by parents from 1968 to 1994. In: Frehsee D, Horn W, Bussmann KD, editors. Family violence against children: a challenge for society. New York: Walter deGruyter; 1996. p. 91-105. Straus MA, Stewart JH. Corporal punishment by American parents: national data on prevalence, chronicity, severity, and duration, in relation to child, and family characteristics. Clin Child Family Psychol Rev 1999;2:55-70. Durrant JE. Evaluating the success of Sweden's corporal punishment ban. Child Abuse Negl 1999;23:435-48.[Medline] Straus MA. Social evolution and corporal punishment. In: Beating the devil out of them: corporal punishment in American families. San Francisco: Jossey-Bass/Lexington Books; 1994. p. 165-88. Larzelere RE, Schneider WN, Larson DB, Pike PL. The effects of discipline responses in delaying toddler misbehavior recurrences. Child Family Ther 1996;18:35-7. Roberts MW, Powers SW. Adjusting chair timeout enforcement procedures for oppositional children. Behav Ther 1990;21:257-71. Edgerton RB. Sick societies: challenging the myth of primitive harmony. New York: Free Press; 1992. Dr. Straus is with the Family Research Laboratory, University of New Hampshire, Durham, New Hampshire.