In this article we examine the effects of self-reported sexual orientation on substance abuse. Using data on a random sample of 6,713 individuals in Washington State, this study examines causes and correlates of substance use by sexual minorities, an at-risk and treatment underserved population. Logistic regression results indicate homosexual orientation is a significant positive predictor of past year marijuana use, past year hard drug use, past year binge drinking, and lifetime alcohol addiction. Bisexual orientation is a significant predictor of past year marijuana use, past year hard drug use, and past year binge drinking. Potential causal mechanisms for these elevated patterns of substance use are discussed.