The relationship between perceived risk of developing AIDS and subsequent behavioral risk status is estimated for 1740 Puerto Rican injection drug users (IDUs). Prospective behavioral effects were examined comparing data collected at mo intervals approximately 6 months apart. We estimated the association between perceived risk at baseline and risky behaviors at follow-up with unadjusted odds ratios. We confirmed the results with adjusted odds ratios using logistic regressions which included baseline risk status as well as socio-demographic and health status covariates. The analyses showed that having a high HIV/AIDS risk perception was related to subsequent sharing of needles, injection of drugs in shooting galleries and sharing of cookers. None of the tests between risk perception and sex risk behaviors showed a significance association. Increasing IDUs' perceived vulnerability to HIV/AIDS might not be effective in helping reduce HIV risk behaviors. IDUs perceiving themselves to be at high risk of AIDS might believe there is little they can do to reverse the consequences of risky behavior.