Friends could be influential on young women's sexual health via influences on sexual behaviours and as connections to sexual partners, but are understudied in sub-Saharan Africa. We cross-sectionally surveyed 2326 13-20 year-old young women eligible for grades 8-11 in rural South Africa about their sexual behaviour and up to three sexual partners. Participants each described five specific but unidentified friends and the relationships between them in an 'egocentric' network analysis design. We used logistic regression to investigate associations between friendship characteristics and participants' reports of ever having had sex (n = 2326) and recent condom use (n = 457). We used linear regression with random effects by participant to investigate friendship characteristics and age differences with sexual partners (n = 633 participants, 1051 partners). We found that it was common for friends to introduce young women to those who later became sexual partners, and having older friends was associated with having older sexual partners, (increase of 0.37 years per friend at least 1 year older, 95% CI 0.21-0.52, adjusted). Young women were more likely to report ever having had sex when more friends were perceived to be sexually active (adjusted OR 1.85, 95% CI 1.72-2.01 per friend) and when they discussed sex, condoms and HIV with friends. Perception of friends' condom use was not associated with participants' reported condom use. While this study is preliminary and unique in this population and further research should be conducted, social connections between friends and sexual partners and perceptions of friend sexual behaviours could be considered in the design of sexual health interventions for young women in South Africa.