Background: Obesity is a known risk factor for the development of postmenopausal breast cancer, specifically hormone-receptor positive breast cancer, and is associated with poor outcomes and decreased overall survival. While obesity in pre-menopausal patients is thought to be protective against the development of breast cancer, application across breast cancer subtypes remains less clear. Methods: We performed a retrospective analysis of 758 patients under 40 years of age diagnosed with breast cancer at our institution over 10 years. Variables including age at diagnosis, breast cancer subtype, race and BMI were evaluated. To assess the association between body mass index (BMI), race and triple negative breast cancer (TNBC), odds ratios (OR) and their associated 95% Confidence interval (CI) OR are reported. Results: Obese patients (BMI >30) were more likely to have TNBC compared with non-obese patients [OR=1.46, 95% CI [1.07 – 2.00), P=0.0161]. Black patients had a twofold likelihood of having TNBC compared with white patients regardless of BMI [OR=2.16, 95% CI [1.56 – 2.97), P<0.0001]. Conclusions: Obese patients under 40 years of age were more likely to be diagnosed with TNBC than non-obese patients. Our data highlights ongoing disparities among TNBC diagnosis and emphasizes the importance of weight loss interventions targeted towards premenopausal women at high risk for breast cancer.