Abstract Background: Gestational diabetes mellitus (GDM) has been hypothesized to increase breast cancer risk, but results from the few prior epidemiologic studies are conflicting, and no studies have examined the association in African American women. Methods: We analyzed data from the prospective Black Women's Health Study to evaluate associations of history of GDM with breast cancer risk among 41,767 parous African American women, adjusting for potential confounders. HRs and 95% confidence intervals (CI) were estimated from multivariable Cox proportional hazards regression models. Results: There was no evidence of an association between history of GDM and risk of invasive breast cancer, overall or by estrogen receptor status. Conclusions: Results of this study do not support the hypothesis that GDM is an important risk factor for breast cancer in African American women overall. Impact: On the basis of these data, breast cancer risk is not increased among African American women with a history of GDM compared with parous women without a history of GDM.