To determine the interpersonal and structural factors associated with receptive syringe sharing (RSS) among female sex workers who inject drugs (FSW-IDU), a group at high risk of HIV/hepatitis C virus (HCV) acquisition. Sex workers And Police Promoting Health In Risky Environments (SAPPHIRE) study, a prospective cohort study. Baltimore, MD, USA PARTICIPANTS: One hundred and eighty FSW-IDU; mean age =33years, 77.1% white and 62.9% in a relationship/married. Surveys were conducted between April 2016 and February 2018. The main outcome was recent RSS (past 3months). In addition to socio-demographic characteristics and drug use behaviors, we assessed factors at the interpersonal level, including injection practices, intimate partner and client drug use and exposure to violence. Structural-level factors included methods of syringe access. Nearly all FSW-IDU used heroin (97.1%) or crack cocaine (89.7%). Recent RSS was reported by 18.3%. Syringes were accessed from needle exchange programs (64.6%), pharmacies (29.7%), street sellers (30.3%) or personal networks (29.1%). Some FSW-IDU had clients or intimate partners who injected drugs (26.3 and 26.9%, respectively). Longitudinal factors independently associated with RSS in the multi-level mixed-effects model were recent client violence [adjusted odds ratio (aOR)=2.17, 95% confidence interval (CI)=1.09-4.33], having an intimate partner who injected drugs (aOR=2.18, 95% CI=0.98-4.85), being injected by others (aOR=4.95, 95% CI=2.42-10.10) and obtaining syringes from a street seller (aOR=1.88, 95% CI=0.94-3.78) or from a member of their personal network (aOR=4.43, 95% CI=2.21-8.90). Client violence, intimate partner injection drug use, being injected by others and obtaining syringes from personal connections appear to increase parenteral HIV/HCV risk among female sex workers who inject drugs.