Men who have sex with men (MSM) account for more than half of all new HIV/AIDS diagnoses in the United States each year, and young MSM (ages 13-24) have the highest increases in new infections. Identifying which young MSM engage in sexual risk-taking in which contexts is critical in developing effective behavioral intervention strategies for this population. While studies have consistently found positive associations between the use of certain drugs and sexual risk, research on alcohol use as a predictor of risk has been less consistent. Participants included 114 young MSM from a longitudinal study of LGBT youth (ages 16-20 at baseline). Participants reported number of unprotected sex acts with up to nine partners across three waves of data collection spanning a reporting window of 18 months, for a total of 406 sexual partners. Sensation seeking was evaluated as a moderator of the effects of both alcohol and drug use prior to sex on sexual risk. Higher levels of sensation seeking were found to significantly increase the positive associations between frequency of unprotected sex and frequency of both alcohol use and drug use with partners. Follow-up analysis found that average rates of alcohol use moderated the association between alcohol use prior to sex and sexual risk, such that decreases in average alcohol use increased the positive association between these variables. Results suggest that while drug use with partners increased sexual risk for all young MSM, the effects of alcohol use prior to sex were limited in low sensation-seeking young MSM as well as those who are high alcohol consumers on average. Implications for future research and behavioral interventions are discussed.