Recent reports have suggested that the use of alcohol or drugs is related to sexual behavior that is high-risk for HIV infection. If substance use leads to unsafe sexual activity, understanding the dynamics of this relationship can contribute to research, preventive and education efforts to contain the spread of AIDS. In this paper, we review research on the relationship between substance use and high-risk sexual behavior. We then consider the inherent limitations of the research designs used to study this relationship, outline some methodological concerns including measurement and sampling issues, and comment on causal interpretations of correlational research findings. We end with a consideration of potential avenues for avenues for future research and a discussion of implications of these findings for current AIDS prevention policies.As the United States enters the second decade of the AIDS epidemic, it has become evident that the primary defense against the spread of this disease is prevention of the behaviors that result in HIV transmission. Recent behavioral research has focused on identification of potentially modifiable variables that may contribute to risk-taking behaviors. One factor that has been proposed as a contributor to sexual risk-taking is the use of alcohol or other drugs with sex (see Leigh, 1990a;Stall, 1988). Because alcohol and drugs are thought to interfere with judgment and decision-making, it has been suggested that their use in conjunction with sexual activity might increase the probability that risky behaviors will occur (e.g., Howard et al., 1988; USDHHS, 1991). In the last few years, a number of reports have appeared suggesting a link between alcohol or drug use and sexual behavior, such as unprotected intercourse, that is known to place an individual at higher risk for HIV infection.In this paper we examine the evidence for and against the hypothesis that a causal relationship exists between alcohol and/or drug use and high-risk sexual behavior for HIV transmission. First, we review research that examines the link between substance use and high-risk behavior, while discussing the limitations of the research designs used to investigate this link. We then consider additional methodological concerns, including measurement and sampling issues, that affect interpretation of research findings. We end with a discussion of implications of these findings for AIDS prevention policies.