The prevalence of serious delinquency varies with age and gender. It increases to a peak at ages 15 to 17, and then decreases markedly for both males and females. Both prevalence and incidence are higher for males than for females. Gender is related to delinquency independently of age and ethnicity. The black-white ratio for delinquency is greater for official measures of delinquency, but not for self-reported delinquency. Further, ethnicity is less strongly related to delinquency than either age or gender. The relations between delinquency and gender, age, and ethnicity can be explained largely by variations in social influences and social reinforcements. More research in this area is needed. 66 references.