Objectives Peers could influence adolescents’ HIV risk and sexual health via connections to sexual partners, sexual behaviour norms, or provision of social support. We investigated associations between young women’s friendships and their Herpes Simplex Virus Type 2 (HSV-2) and HIV infection status in rural South Africa. Design Cross-sectional, egocentric network analysis of HPTN 068 baseline. Methods In 2011-2012, we tested 13-20 year-old young women for HIV and HSV-2 and collected descriptions of five friendships for each. We generated summary measures describing the socio-demographic characteristics and the number of friends perceived to have had sex. We used logistic regression to analyse associations between friend characteristics and participant HIV and HSV-2 infection. Results There were 2326 participants included in the study sample, among whom HIV and HSV-2 prevalence were 3.3% and 4.6% respectively. Adjusted for participant and friend socio-demographic characteristics, each additional friend at least one year older than the participant was associated with raised odds of HIV (OR= 1.37, 95% CI 1.03-1.82) and HSV-2 (adjusted OR=1.41, 95% CI 1.18-1.69). Each additional friend perceived to have ever had sex also raised the odds of HIV (OR= 1.29, 95% CI 1.03-1.63) and HSV-2 (OR=1.18, 95% CI 1.03-1.35). Conclusion We found evidence that a greater number of older friends and friends perceived to have had sex were associated with increased risk for HSV-2 and HIV infection. While further longitudinal research would assist in disentangling any causal relationships, the extent to which policies or programmes influence age-mixing and young people’s normative environments should be examined.