A multidimensional measure assessing distinct motivations for and against sex was shown to be reliable, valid, and configurally invariant among incoming first-year college students. Three Motivations Against Sex Questionnaire subscales were developed to measure motivations against sexual behavior (Values, Health, Not Ready) to complement and extend a set of Sexual Motivations Scale–Revised subscales assessing motivations for sexual behavior (Intimacy, Enhancement, Coping). Participants were surveyed the summer prior to college (N = 1,653; 58.4% female). Exploratory factor analysis on a random one quarter of respondents supported the hypothesized factors. Multigroup confirmatory factor analysis demonstrated good overall fit to the data and configural invariance across gender and ethnicity and across lifetime sexual experience. Motivations were associated with lifetime oral and penetrative sexual behaviors. This combined measure may be used for identifying motivations, predicting behaviors, and tailoring motivational interventions for sexual health among adolescents and young adults.