Background African American women are disproportionately affected by HIV/AIDS. Concurrent sexual partnerships may contribute to racial disparities in HIV infection. Little is known about attitudes and practices related to concurrency among African American women, or the social, structural and behavioural factors influencing concurrency. Methods: We recruited 19 heterosexual African American women engaging in concurrent sexual partnerships from a public clinic in Philadelphia in 2009. We conducted interviews exploring social norms, attitudes and practices about concurrency, and the structural, social and behavioural factors influencing concurrent sexual partnerships, guided by grounded theory. Results: Seventeen women reported one main and one or more non-main partners; two reported no main partners. Many women used condoms more frequently with non-main than main partners, noting they trust main partners more than non-main partners. Social factors included social normalisation of concurrency, inability to negotiate partners' concurrent partnerships, being unmarried, and not trusting partners. Lack of trust was the most commonly cited reason that women engaged in concurrent partnerships. Structural factors included economic dependence on partners, partners' dependence on women for economic support and incarceration that interrupted partnerships. Behavioural factors included alcohol and cocaine use. Conclusions: Social, structural and behavioural factors strongly influenced these African American women's concurrent sexual partnerships. Many HIV interventions disseminated by the CDC focus largely on behavioural factors and may fail to address the social and structural factors influencing African American women's sexual networks. Novel HIV prevention interventions that address the social determinants of African American women's HIV risks are urgently needed.