The impact of victim and offender preassault substance use on the outcomes of sexual assault incidents was analyzed. Nine hundred and seventy female sexual assault victims were identified from the first wave of a longitudinal study based on a convenience sampling strategy. Multivariate models showed that victim injury was more likely in assaults involving offender substance use (regardless of whether or not the victim was also using substances). Offender use of physical force and verbal threats were also related to greater odds of completed rape and injury, and force was associated with medical attention seeking. Based on this study, rape prevention programs should target men and focus on the role of substance use in sexual assault. These prevention programs should incorporate information on the roles of offender and victim substance use, offender aggression, and other situational factors in sexual assault outcomes. Study limitations and suggestions for future research on the role of victim and offender substance use in rape incidents are presented. (Contains 2 tables.)