This study investigated differences in drug use and sexual behaviors among from 237 male and 123 female heroin users in Dar es Salaam, Tanzania. Multivariate models of risk of needle sharing were estimated using multivariate logistic regression. Men were significantly older, more likely to inject only white heroin, share needles, and give or lend used needles to other injectors. Women were more likely to be living on the streets, have injected brown heroin, have had sex, have had a higher number of sex partners, and have used a condom with the most recent sex partner. Being male and earning less than US $46 in the past month were significant predictors of increased risk of needle sharing. Despite differences in sociodemographic, drug use, and sexual behaviors by gender, both male and female injectors in Dar es Salaam exhibit elevated risk of HIV infection associated with drug use.