Background. Male breast cancer accounts for less than 1% of all breast cancers, yet males have a worse prognosis than females with breast cancer. Methods. Using the 1988-2003 Surveillance, Epidemiology, and End Results Program data, we conducted a retrospective, population-based cohort study to investigate stage-specific differences in breast cancer-specific and allcause mortality between males and females. We calculated adjusted hazard ratios (aHR) and 95% confidence intervals (CI) using Cox regression models to compare breast cancer-specific and all-cause mortality by stage between males and females, controlling for potential confounding variables. Results. There were 246,059 patients with a first, single, primary breast cancer [1,541 (0.6%) male; 244,518 (99.4%) female]. Compared with females, males were more likely to be older, Black, married, diagnosed at more advanced stages, and treated with mastectomy (each P<0.001). Males also were more likely to have lower grade and estrogen/progesterone receptor-positive tumors (each P<0.001). After controlling for confounders, males were more likely to die from their breast cancer when compared with females, only if diagnosed with stage I disease (aHR 1.72, CI 1.15-2.61). For all-cause mortality, males were more likely than females to die at each stage of disease except stage IV. Conclusions. Although all-cause mortality was higher for men than women at all stages of nonmetastatic breast cancer, higher male breast cancer-specific mortality was attributed to poorer survival in stage I disease. However, this statistical difference is unlikely to be clinically relevant and attributable to in-stage migration.