The contribution of type 2 diabetes and obesity on mortality in breast cancer (BC) patients has not been well studied among Hispanic women, in whom these exposures are highly prevalent. In a multi-center population-based study, we examined the associations between diabetes, multiple obesity measures, and mortality in 1180 Hispanic and 1298 non-Hispanic white (NHW) women who were diagnosed with incident invasive BC from the San Francisco Bay Area, New Mexico, Utah, Colorado, and Arizona. Adjusted hazard ratios (HR) and 95 % confidence intervals (CI) were calculated using Cox proportional hazards regression models. The median follow-up time from BC diagnosis to death was 10.8 years. In ethnic-stratified results, the association for BC-specific mortality among Hispanics was significantly increased (HR 1.85 95 % CI 1.11, 3.09), but the ethnic interaction was not statistically significant. In contrast, obesity at age 30 increased BC-specific mortality risk in NHW women (HR 2.33 95 % CI 1.36, 3.97) but not Hispanics (p-interaction = 0.045). Although there were no ethnic differences for all-cause mortality, diabetes, obesity at age 30, and post-diagnostic waist-hip ratio were significantly associated with all-cause mortality in all women. This study provides evidence that diabetes and adiposity, both modifiable, are prognostic factors among Hispanic and NHW BC patients.