The findings show that young women were more likely than the men to initiate physical aggression in late adolescence; however, by their mid-20s, there were no significant gender differences in the rates of initiating physical aggression. The average rates of reciprocating physical aggression initiated by the partner across the four time points were similar for men and women. Women and men were apparently more likely to report injuries from physical aggression with a partner if the couples engaged in mutual physical aggression. The study used data from the Oregon Youth Study (OYS), a community-based sample of 206 young men at risk for delinquency and the Couples Study of the OYS men and their intimate partners. The Couples Study assessed the men and their partners four times over the study years: later adolescence (ages 17-20 years), young adulthood (ages 20-23), and early adulthood (ages 23-25 and 25-27 years). Assessments for the OYS included interviews of the parents and the young man, self-report questionnaires, and interviewer ratings. Assessments for the Couples Study included a separate interview and questionnaires for the OYS men and their partners and a videotaped session composed of a series of interactive tasks that varied across the four time points. 5 tables and 45 references