The present study examined the relationship among acculturation, familismo, and HIV-related adolescent sexual risk behavior. Data were collected from Latino mother-adolescent dyads to permit parent and adolescent analyses of familismo for predicting oral, vaginal, and anal sexual behaviors. A random sample of 702 Latino eighth-grade students and their mothers was recruited from New York City. The sample included Mexicans (n = 203), Puerto Ricans (n = 239), and Dominicans (n = 260). Acculturation was unrelated to sexual behavior, but adolescent familismo was related to girls' but not boys' sexual behavior. The most important facet of familismo was subjugation to the family, which was negatively associated with girls' sexual behavior. The implications for HIV prevention programs for Latino youth are discussed.