Homosexual men and women have been described as at high risk for alcohol and drug abuse, due to psychosocial variables such as stress levels or the cultural importance of bar settings. However, there are few actual data in this regard. This paper presents the findings of a large (n = 3400) survey of a homosexual population regarding population characteristics and patterns of alcohol and drug use. Psychosocial variables that may account for substance use patterns both generally and in this population are discussed in an accompanying paper. Substantially higher proportions of the homosexual sample used alcohol, marijuana, or cocaine than was the case in the general population. Contrary to other reports, this was not accompanied by higher rates of heavy use, although homosexuals did show higher rates of alcohol problems. In the general population women consume less drugs and alcohol than do men, and substance use substantially declines with age. Neither of these patterns were found for the homosexual sample, thus creating overall higher rates of substance abuse. This may reflect differences between homosexuals and the general population in their adherence to sex-role stereotypes and age-related social role changes, as well as culturally specific stressors and vulnerability to substance use.