Background: Female drug users are more likely to transmit human immunodeficiency virus (HIV) to their sexual partners. Little is known about HIV, sexually transmitted diseases (STDs), cervicitis, and drug abuse among female sex workers in Iran. Objectives: Therefore, this study was conducted at a Drop-in center (DIC) in Iran to investigate the prevalence of HIV associated risk factors, the prevalence of drug use, high-risk sexual behaviors, and the relationship between the associated factors in women. Patients and Methods: This quantitative cross-sectional study was conducted on 190 female sex workers (SW) in a DIC in Sari, Mazandaran, Northern Iran, in January and February 2014. The study sample was selected through census sampling. In the end, 190 female SWs referring to the DIC participated in our study. There was no limitation in sampling. The self-administered questionnaire was completed via an interview. Results: The results showed that 39% of the female SWs were less than 30 years old and 64% had elementary school education. In addition, 59% of the participants took some type of illegal drugs and 1. 1% of them were reportedly injecting drug users. Moreover, 43% of them had substance dependent husbands, and 39% were reportedly regular condom users. They had 1-10 sexual partners on average per week. The overall prevalence of HIV infection was 4%. A significant relationship was found between the type of drugs used and factors such as having a substance dependent husband, use of condom during the last sexual contact, regular condom use, and the number of sexual acts per week. A significant correlation exists between using psychiatric drugs and factors like regular condom use, education, cervicitis, and the number of sexual conducts per week. Conclusions: Female sex workers often engage in sex for financial reasons and are at high risk of drug abuse, HIV, and cervicitis. In addition, the rate of cervicitis among females with high-risk sexual behavior is considerable in Mazandaran, Iran. Therefore, the state authorities should provide sex workers with health care services and help them acquire a good job to support their life.