Methamphetamine use has become a major problem among communities of men having sex with men (MSM), where it has been associated with high-risk behaviors. Methamphetamine is often combined with other drugs that may increase its risks and adverse health consequences. To examine differences in background characteristics, HIVrisk behaviors, and psychosocial variables among polydrug-using HIV-positive MSM, the researchers classified a sample of 261 HIV-positive, methamphetamine-using MSM into three user groups: (1) methamphetamine only; (2) methamphetamine, marijuana, and poppers (light polydrug users); and (3) methamphetamine and other drugs (e.g., cocaine, heroin, hallucinogens, and ketamine; heavy polydrug users). Only 5% reported using only methamphetamine during the past 2 months; 31% were classified as light polydrug users, and 64% were classified as heavy polydrug users. Heavy polydrug users were significantly younger than light polydrug users (35.6 vs. 38.4, P<.01) and reported using methamphetamine for significantly fewer years (10.3 vs. 14.2 years, P<.001), but did not differ in the amount and frequency of methamphetamine or alcohol consumed. Heavy polydrug users reported significantly more sex partners of HIV-negative and unknown serostatus and had more unprotected sex with these partners. Heavy polydrug users had significantly higher scores on impulsivity and negative self-perceptions, as compared with those of light polydrug users. In this sample of HIV-positive MSM, most of those who used methamphetamine had a pattern of polydrug use. Heavy polydrug users reported significantly more high-risk sexual behaviors and tended toward higher levels of impulsivity than light polydrug users. The implications of these findings are two-fold: (1) Longitudinal research is needed to establish causal relationships among methamphetamine use, impulsivity, negative self-perceptions, and sexual risk behavior in this target population; (2) behavioral interventions should evaluate whether methamphetamine use and sexual risk behavior can be reduced by modifying impulsivity and negative self-perceptions.