This study examined the role of religiousness and gender in age at first intercourse, and sexual expectations and values in Mexico, a macrocontext where the majority is Mexican and Catholic (83%). Participants were Catholic and nonreligious adolescents (54% girls) attending middle (71%) or high school. Findings indicated that Catholic adolescents engaged in sexual intercourse at later ages than nonreligious adolescents. Both religious attendance and importance of religion and values in sexual decision making were associated with more conservative sexual values. Boys who were raised Catholic were more likely to endorse female virginity values and were less likely to expect to wait to have sex until married than nonreligious boys. These associations were not significant among girls. Catholic boys may be more likely to internalize sexual double standard beliefs regarding premarital sex than nonreligious boys. This study expands our understanding of the role of religiousness in Mexican adolescents' sexuality.