Data were obtained from 526 dating couples at a large midwestern university and from a national probability sample of 237 cohabiting and 5,005 married couples. Cohabiting couples had a higher rate of assault than dating or married couples, even after controls for age, education, and occupational status were introduced. Violence in cohabiting couples was also more severe than in dating or married couples. Factors that may account for more frequent violence in cohabiting relationships include social isolation, autonomy and control, and investment in the relationship. 57 references, 3 tables, 5 figures. (Author abstract modified)