This study investigates whether high-risk young adults' perceptions of their likelihood of living to age 35 and of acquiring HIV are related to their substance abuse problems and risky sexual behaviors. The sample consists of data from the 72- and 87-month follow-up assessments of 449 juvenile offenders referred to probation in 1999 and 2000. Results indicate that believing one is likely to get HIV is associated with having more concurrent substance use problems and engaging in more risky sexual behaviors. Longitudinal analyses indicate that youth who think they are likely to get HIV are at greater risk for later substance abuse problems and risky sexual behaviors, though these results are only marginally significant. The results demonstrate that respondents are aware of some of the risks associated with their recent substance using and sexual behaviors, but that holding these perceptions does not result in a reduction of these behaviors. (Contains 3 tables, 1 figure, and 2 notes.)