OBJECTIVE: Sexual liaisons between older men and younger women have been linked to greater risk of HIV acquisition. This study aims to (1) identify psychosocial and behavioral factors associated with age-discordant (partner >/=5 years) versus age-concordant partnerships (-1< partner <5) and (2) examine the association between partner age discordance and young South African women's sexual behavior. METHODS: We used generalized estimating equations to analyze responses from 656 sexually experienced women (aged 13-20 years) from rural Mpumalanga province. RESULTS: Partner age discordance was associated with greater odds of reporting both more frequent sex [adjusted odd ratio (aOR) = 1.77; 95% confidence interval (CI): 1.20 to 2.60] and having a partner with concurrent partnerships (aOR = 1.77; 95% CI: 1.22 to 2.57). Age-discordant partnerships were associated with greater odds of casual partnerships (aOR = 1.50; 95% CI: 1.06 to 2.13), having a partner with concurrent partnerships (aOR = 1.71; 95% CI: 1.19 to 2.46), and more frequent intercourse (ie, having sex at least 2 or 3 times per month) (aOR = 2.04; 95% CI: 1.39 to 3.00). They were associated with lower odds of reporting condom use at last sex (aOR = 0.70; 95% CI: 0.50 to 0.98) and always using condoms (aOR = 0.53; 95% CI: 0.32 to 0.88) in age-discordant partnerships. CONCLUSIONS: Our findings suggest that a history of age-discordant partnerships, and to a lesser extent having an age-discordant partner, is linked to HIV risk among young South African women; however, the link between partner age discordance and HIV risk may be more strongly related to the characteristics of age-discordant partnerships than to the characteristics of young women who form such partnerships.