This study examines the prevalence of crack use among out-of-treatment drug users in the San Juan metropolitan area. Of the sample of 849 drug users, 310 (36.5%) were crack users only, 179 (21.1%) were drug injectors and crack users, and 360 (42.4%) were drug injectors only. To study the characteristics of crack users we selected the subjects who reported the use of crack only. Of the 310 subjects, 193 (62.3%) men and 117 (37.7%) women, the mean age was 29 years. Significant differences were observed by gender. Females reported higher education, living in a nuclear family, crack/cocaine as the first drug used, history of sexually transmitted diseases and higher rates of HIV seropositivity. Males were more likely to report income from illegal activities, incarceration, use of multiple drugs, and more years of drug use. Among those sexually active, females were more likely to practice unprotected vaginal sex, have multiple sex partners, engage in prostitution (exchange of sex for money and/or drugs) and use condoms.