Research indicates an association between marital status and health but this link has not been thoroughly explored. Our goal was to examine the association of marital status on the diagnosis, treatment, and survival of older women with breast cancer and the potential role socioeconomic status, education level, and comorbidities may play in explaining these associations. Retrospective cohort study using linked Medicare and National Cancer Institute Surveillance, Epidemiology, and End Results cancer registry. The sample consisted of 32,268 women aged 65 years and older who received a diagnosis of breast cancer from 1991 to 1995. Information available through 1998 allowed for 3 years of follow-up. Results showed that unmarried women were more likely to be diagnosed with breast cancer stage II-IV versus stage I and in situ (OR 1.17; CI95 1.12, 1.23). Unmarried women diagnosed with stage I or II breast cancer were less likely to receive definitive therapy (OR 1.24; CI95 1.17, 1.31). Even after controlling for cancer stage and size at diagnosis and treatment received, unmarried women were at an increased risk of death from breast cancer (HR 1.25; CI95 1.14, 1.37). Socioeconomic variables and comorbidity had little impact on the relationship between marital status and survival. Older married women were at decreased risk for mortality after a diagnosis of breast cancer. Many of the health benefits enjoyed by married women are likely derived from increased social support and social networks.