Background: In Zimbabwe, adolescent girls and young women (AGYW) experience high rates of HIV and other sexual and reproductive health challenges. In 2013, the Zimbabwe Ministry of Health and Child Care partnered with the United Nations Population Fund to implement the Sista2Sista programme, a structured peer group intervention aimed at improving health outcomes among vulnerable in-and out-of-school AGYW. Methods: Programme data was analysed for 91 612 AGYW aged 10-24 years old who participated in Sista2Sista from 2013 to 2019. Logistic regression was used to determine odds ratios (OR) and evaluate programme exposure as a factor in a set of defined variables. Results: 58 471 AGYW (63.82%) graduated from the Sista2Sista programme by completing at least 30 of 40 exercises. Graduates were more likely to take an HIV test (2.78 OR 95% CI 2.52-3.10), less likely to get married (0.63 OR 95% CI 0.55-0.73) and less likely to drop out of school (0.60 OR 95% CI 0.53-0.69). At higher thresholds of programme completion, additional positive outcomes were observed. Participants who completed all 40 exercises were more likely to return to school (1.41 OR 95% CI 1.18-1.69), more likely to use contraception (1.38 OR 95% CI 1.21-1.56), more likely to report sexual abuse (1.76 OR 95% CI 1.17-2.66), and less likely to become pregnant as adolescents (0.41 OR 95% CI 0.24-0.72). Individual counselling improved the likelihood of programme graduation. Conclusions: The Sista2Sista programme had a positive effect on HIV and other sexual health outcomes among vulnerable AGYW in Zimbabwe. Strategies to improve graduation rates should be explored.