This study describes the distribution, nature, pattern, and magnitude of sex differences in self-report delinquency. A national probability sample of 1725 youths, ages 11-17, was interviewed using a comprehensive measure of self-report delinquency including serious and violent crimes. Major findings include (1) small but consistent sex differences in numerous delinquent behaviors and in most types of delinquent behavior due to higher offense frequencies of males and greater numbers of male offenders, (2) generally similar patterns of male and female delinquency (r = .82).(3) sex differences in the proportion of high-frequency offenders, (4) few interaction effects of sex with other demographic variables, and (5) stable sex differences in certain delinquent acts across a decade.The debate over the nature, magnitude, and distribution of sex differences in delinquency continues, despite a proliferation of studies. While there is general agreement between official and self-report studies that males are involved in more delinquency than females, there is widespread disagreement over the magnitude and nature of the sex difference. Indeed, the controversy extends to the very method (official or selfreport measures) that is best suited to resolve the debate.Studies using official and self-report measures of delinquency agree that males are involved in substantially more delinquent behavior than females, but disagree as to the magnitude of this difference. In official statistics malejfemale ratios generally fall within the range of 3:l to 7:l (Cockburn and Maclay, 1965;Edwards, 1973;Wattenberg and Saunders, 1954;Wolfgang, 1979). The 1978 Uniform Crime Reports indicate a maldfemale ratio of 3.6:l for youth under 18 (US. Department of Justice, 1979). Malejfemale ratios observed in self-report delinquency AUTHORS NOTE: The author i s indebted to Drs. D. Wayne Osgood, David Huizinga, and Hart Weichselbaum for their valuable comments on earlier drafts of this article.