Theories of health behavior change suggest that perceived susceptibility to illness precedes health-protective behavior. We used a cross-lagged panel design to explore the relationship between perceived susceptibility to AIDS, and HIV risk behavior pre-incarceration and post-release in a sample of 499 jail inmates, a group at high risk for HIV. We also explored moderators of this relationship. HIV risk was calculated with a Bernoulli mathematical process model. Controlling for pre-incarceration HIV risk, perceived susceptibility to AIDS predicted less post-release HIV risk; the reverse relationship was not supported. Consistent with health behavior change theories, perceived susceptibility seemed to partially guide behavior. However, this relationship was not true for everyone. African-Americans and individuals high in borderline personality features exhibited no relationship between perceived susceptibility and changes in HIV risk. This suggests that targeted interventions are needed to use information about risk level to prevent HIV contraction.