The purpose of this research was to investigate moral reasoning related to sexual behavior that could lead to the transmission of sexually transmitted diseases (STDs). Using hypothetical dilemmas about situations in which STDs can be transmitted, respondents were asked to explain why they believed the characters should or should not engage in risky behaviors. 40 college freshmen (M = 18.3 years) and 32 college seniors (M = 22.3 years) participated. Using Kohlberg's moral stage theory and Gilligan's moral orientation model, the interviews were scored for moral stage and moral orientation. Results indicated that the older age group had a significantly higher stage of moral reasoning than the younger age group when responding to dilemmas about STDs. There was a significant difference in moral stage between dilemmas, reflecting the possible effect of dilemma content on moral reasoning. The overall pattern of results shows nonsignificant gender differences in stage of moral reasoning and moral orientation. Clinical and theoretical implications of these findings for understanding the role of moral reasoning in sexual risky behavior are discussed.