The objectives of the current study were to determine the incidence and prevalence of hard-core drug (HCD) use and to explore the predictors of HCD use in a three-wave longitudinal study of women ages 18-35 living in urban areas of high drug traffic in Puerto Rico. Prevalence of HCD use was determined by positive self-report or positive toxicological tests for crack, cocaine, or heroine at baseline and follow-up periods. Incidence density was calculated using Poisson methods. Predictors of HCD use were identified using the generalized estimating equation (GEE) approach. Prevalence rates fluctuated between 16.3 at baseline and 12.6 and 14.6 at subsequent waves. Incidence of crack/cocaine or heroine ranged from 7.4 to 6.3 per 100 person years. Low education, unemployment, current alcohol use, and severe partner violence predict incident HCD use. Therefore, prevention programs for HCD use must consider strategies to promote social mobility and empowerment and to mitigate violence against women.