Background: The ER-/PR-/HER- (triple negative or TN), and ER-/PR-/HER+-(HER2-overexpressing) subtypes have the highest risk of breast cancer mortality for all race/ethnicities. Younger age is known to increase the risk of the TN subtype but how age affects the risk of mortality within a race/ethnicity and subtype is unknown. The purpose of this study is to assess the affect of age on the risk of breast cancer specific mortality within four mutually exclusive categories of race/ethnicity within the TN and HER-2 overexpressing subtypes. Methods: Using the population based California Cancer Registry, we identified 22,254 cases of TN and 11,348 cases of the HER2 overexpressing subtypes with stages 1-4 first primary female invasive breast cancer diagnosed between January 1, 2000 and December 31, 2013. Cases were identified as white (n = 18,793), black or African American (n = 3,479), Hispanic (n = 7,171) and Asian/Pacific Islander (API) (n = 4,159). Cox regression analysis adjusted for stage, grade, socioeconomic status, and treatment was used to compare the risk of breast cancer specific mortality for women ≤ 45 years (younger) of age and ≥ 70 years of age (older) when compared with women aged 46-69 within each of the four race/ethnicities for each of these subtypes. Results: Older white (HR = 1.52; 1.37-1.68), Hispanic (HR = 1.28; 1.04-1.58), and API women (HR = 1.50; 1.11-2.03) with the TN subtype had an increased risk of mortality. Older white (HR = 1.53; 1.32-1.77) and Hispanic women (HR = 2.33; 1.78-3.05) with the HER2-overexpressing had an increased risk of mortality whereas older API women had the same risk of mortality as younger women. Age was not a significant risk factor of mortality for African American women with the TN and HER2-overexpressing subtypes. Conclusions: In contrast with other ethnicities, the risk of mortality for black women with the TN and HER2-overexpressing subtypes is the same regardless of age.