Concurrent sexual partnerships are increasingly recognized as an important behavioural driver of HIV epidemics, particularly in southern Africa. The prevalence of HIV among young people in South Africa can be reduced by decreases in sexual risk behaviours, including engaging in concurrent partnerships. This analysis examines the frequency and correlates of concurrency in a representative multi-racial young adult (aged 16-26) population in the Cape Metropolitan Area, using multivariate logistic regression. Overall, approximately 13% of sexually active young adults reported concurrency during their last sexual partnership, though there was significant variability by sex and race, ranging from 33% of young Black men to 2% of young Coloured women reporting concurrency. Concurrency was associated with other high risk behaviours, including a higher number of lifetime sex partners and a lower age of sexual debut. Future prevention effects among young adults will need to address concurrency in order to minimize the risk of HIV infection.