Young female sex-workers (FSW) aged 18-24 are at high risk of HIV due to high numbers of sexual partners, difficulty negotiating condom use, increased risk of gender-based violence, and limited access to services. Here we describe changes in sexual behaviours among young FSW across Zimbabwe between 2013 and 2016, and risk factors for prevalent HIV in 2013 and 2016. FSW ≥ 18 years were recruited using respondent-driven sampling in 14 sites across Zimbabwe in 2013 and 2016 as part of the SAPPH-IRe trial. We collected data on socio-demographics and sexual behaviour and offered HIV testing. Statistical analyses were RDS-II weighted. Characteristics of young FSW aged 18-24 were described, stratified by age. Logistic regression was used to assess difference in sexual behaviours by reported HIV status between 2013 and 2016, and to explore associations with prevalent HIV in 2013 and 2016. 656 young FSW were recruited in 2013 and 503 in 2016. Characteristics of young FSW were similar across both surveys. HIV prevalence was similar at both time points (35% vs 36%) and rose steeply with age. Compared to young FSW in 2013, reported condom-less sex with a steady partner and condom-less sex with clients was higher in 2016 among women self-reporting HIV negative status (OR = 6.41; 95%CI: 3.40-12.09; P<0.001) and (OR = 1.69; 95%CI: 1.14-2.51, P = 0.008), respectively, but not among young FSW self-reporting HIV positive status (OR = 2.35; 95%CI: 0.57-9.76; P = 0.236) and (OR = 1.87; 95%CI: 0.74-4.74; P = 0.186). After adjusting for age in 2016, young FSW who had ever been married had increased odds of testing HIV positive (OR = 1.88; 95% CI 1.04-3.39; P = 0.036) compared with those who had never married. Young FSW who completed secondary education or higher were less likely to test HIV positive (OR = 0.41; 95% CI 0.20-0.83; P = 0.012) compared with those with primary education or less. Young FSW remain at very high risk of HIV. Strategies to identify young FSW when they first start selling and refer them into services that address their economic, social and sexual vulnerabilities are critical.