Purpose: Breast tumors from young women under the age of 40 account for approximately 7% of cases and have a poor prognosis independent of established prognostic factors. We evaluated the patient population served by the Military Health System, where a disproportionate number of breast cancer cases in young women are seen and treated in a single universal coverage healthcare system. Methods: The Military Health System Repository and the DoD Central Registration databases were used to identify female breast cancer patients diagnosed or treated at military treatment facilities from 1998 to 2007. Results: 10,066 women were diagnosed with invasive breast cancer at DoD facilities from 1998 to 2007, of which 11.3% (1139), 23.4% (2355) and 65.2% (6572) were OpenSPiltSPi 40, 40–49 and CloseSPigtSPi 50 years old (yo), respectively, at diagnosis. 53% in the OpenSPiltSPi 40 yo cohort were white, 25% were African American (AA) and 8% were Hispanic, with 14% undisclosed. Breast cancer in women diagnosed OpenSPiltSPi 40 yo was more high grade (p OpenSPiltSPi 0.0001), Stage II (p OpenSPiltSPi 0.0001) and ER negative (p OpenSPiltSPi 0.0001). There was a higher rate of bilateral mastectomies among the women OpenSPiltSPi 40 compared to those 40–49 and CloseSPigtSPi 50 (18.4% vs. 9.1% and 5.0%, respectively). Independent of disease stage, chemotherapy was given more frequently to OpenSPiltSPi 40 yo (90.43%) and 40–49 yo (81.44%) than ≥ 50 yo (53.71%). The 10-year overall survival of younger women was similar to the ≥ 50 yo cohort. Outcomes in the African American and Hispanic subpopulations were comparable to the overall cohort. Conclusion: Younger women had a similar overall survival rate to older women despite receiving more aggressive treatment.