OBJECTIVES: Marital status has been shown to affect outcomes in patients with multiple types of malignance, including breast cancer in women over the age of 65.  The purpose of this study is to investigate the effect of marital status on diagnosis, treatment, and survival of women with breast cancer under the age of 65.   METHODS: The Survey of Epidemiology and End Results (SEER) database was queried for all women ages 25-64 with a diagnosis of invasive breast cancer from the years 2004-2009.  Chi-square analysis was used to examine the association of marital status and age, race, stage, estrogen receptor positivity, tumor size, tumor grade, and choice of breast operation.  Logistic regression was used to predict late stage diagnosis by marital status and Cox proportional hazards models were used to compare survival by marital status classification adjusting for age, race, AJCC stage, and ER positivity. RESULTS: Unmarried women were more likely to be older, Black, diagnosed at a later stage, and with larger tumors.  There was no difference in choice of breast surgery between married and unmarried women.  Unmarried women were 1.18 times more likely to be diagnosed at a later stage (stage 2 or higher) than married women after adjusting for age, race, and ER positivity (OR = 1.18, 95% CI 1.15, 1.20).   Unmarried women were 1.33 times more likely to die compared to married women after adjusting for age, race, AJCC stage, and ER positivity (HR 1.33, 95% CI 1.29, 1.37). CONCLUSIONS: Unmarried women are more likely to present with more advanced disease and have a higher risk of death from breast cancer.  Attention should be paid to marital status in young women at the time of diagnosis.  Unmarried women may benefit from additional counseling, psychosocial support, and case management to ensure their overall outcomes are optimized.