Partner-age difference is an HIV-risk factor among young women in Africa, but the underlying mechanisms are poorly understood. We used nationally representative data among black South Africans (men: 3,530; women: 3,946) to examine the proportion of women in partnerships involving male partner concurrency by age of female partners and by age-disparate (≥5 years) partnerships. Of all partners reported by men, 35 % of young (16-24) women were in partnerships involving male partner concurrency of 4 weeks or longer during the past 12 months. Young women in age-disparate partnerships were more likely to be in partnerships with men who had other concurrent partners (9 %; OR 1.88 p < 0.01) and more likely to be connected to an older sexual network. Our results suggest that the relationship between male concurrency and age-disparate relationships may increase HIV risk for young women by connecting them to larger and older sexual networks.