This article reports results of a randomized controlled trial designed to test an intervention to increase parent-adolescent sexual risk communication among Mexican parents. Data were analyzed from parents (n = 791) randomly assigned to an HIV risk reduction or health promotion intervention. Measures were administered at pretest, posttest, and 6- and 12-month follow-ups. Generalized estimation equation (GEE) analysis indicates parents in the HIV risk reduction intervention reported significantly more general communication (p less than .005), more sexual risk communication (p less than .001) and more comfort with communication (p less than .001) than parents in the control intervention. Behavioral, normative, and control beliefs significantly mediated the effect of the intervention on all communication outcomes. This study demonstrates the efficacy of an intervention to increase the quality and quantity of parent-adolescent communication related to general and sex-specific communication.