People’s motives for casual sex moderate associations between their sexual behavior and the outcomes they experience. Derived from self-determination theory, autonomous motives for casual sex (e.g., I wanted the fun and enjoyment) and non-autonomous motives (e.g., I wanted to please someone else) correlated in previous research differentially with measures of well-being and incidence of casual sex. In a sample of American college students (N = 284), we replicated these prior findings and extended them as follows: autonomous and non-autonomous motives for sex were correlated with two measures of casual sex (i.e., the three behavior questions from the Sociosexual Orientation Inventory; the number of partners with whom participants had penetrative sex but did not wish to become emotionally involved); two measures of well-being (i.e., self-esteem, depression), and a measure of overall sexual victimization (i.e., a combined score from the Sexual Experiences Survey). We found that autonomous motives were more strongly associated with casual sexual behavior than were non-autonomous motives in both sexes. Autonomous motives were positively associated with sexual victimization in women but not in men. Compared to autonomous motives, sex for non-autonomous motives was linked to less self-esteem in both sexes, and with more depression and sexual victimization in women. Sex differences in associations between motives and victimization persisted even when the general effects of participant’s sex and casual sex were controlled in hierarchical regressions. Our findings further revealed the importance of agency (or lack thereof) in predicting sexual behavior and psychological health.