The objective of this study was to compare human immunodeficiency virus (HIV) risk factors among female street youths involved in prostitution and those with no history of prostitution. Youths aged 14 to 25 years were recruited into the Montreal Street Youth Cohort. Semiannually, youths completed an interviewer-administered questionnaire. Statistical analyses comparing characteristics and HIV risk factors for girls involved in prostitution and those never involved were carried out using parametric and nonparametric methods. Of the girls, 88 (27%) reported involvement in prostitution, and 177 girls reported no history of prostitution at the baseline interview. Girls involved in prostitution were two times and five times more likely to have reported bingeing on alcohol and on drugs, respectively. A history of injection drug use was four times more likely to have been reported by girls involved in prostitution. Further, these girls were 2.5 times more likely to have reported injected cocaine as their drug of choice. Girls involved in prostitution were younger the first time they had consensual sex and were twice as likely to have reported anal sex. Consistent condom use for anal, vaginal, and oral sex was low for all girls. Girls involved in prostitution reported more risky sexual partners. In conclusion, girls involved in prostitution may be at increased risk of HIV infection due to their injection drug use and risky sexual behaviors. Unique intervention strategies are necessary for reducing HIV infection among female street youths involved in prostitution.