Data were obtained from the National Youth Survey, a longitudinal study of self-reported problem behavior. The initial sample of 1,725 respondents was chosen from a national probability sample of households in the continental United States, based on a multistage cluster sampling design. The study began in 1976 when respondents were between 11 and 17 years of age and included 9 waves of data over a 17-year period. Overall completion rates were 90 percent for the first 3 waves, above 80 percent for waves 4 through 8, and 78 percent for wave 9. The study examined data from the four most recent surveys for which information on violence between male and female married or cohabiting respondents was available in the following years: 1983, 1986, 1989, and 1992. Results confirmed previous findings of extensive violence by women, with little evidence of systematic over-reporting or under-reporting by either men or women. Although both men and women engaged in frequent minor assaults, men were more likely than women to repeatedly beat their partner during the course of a year. In addition, women were far more likely than men to suffer physical injury and seek medical treatment. Taken together, the findings somewhat reconcile the discrepancy regarding partner assault; women are more often than men the victims of severe partner assault and injury, not necessarily because men strike more often but because men strike harder. 53 references, 3 notes, and 9 tables