OBJECTIVES: Many elderly women with early-stage breast cancer (BC) receive mastectomy when breast-conserving surgery (BCS) plus radiation therapy (RT) is an option, or do not receive recommended RT following BCS. This study examined associations with primary treatment (BCS+RT, mastectomy, or BCS without RT) for early-stage BC among elderly women. METHODS: A sample of 26,106 women age > 66 diagnosed with invasive early-stage BC from 2003 to 2006 were selected from the SEER-Medicare linked dataset. Multivariate logistic regression models examined the relationship between type of treatment and various independent factors. RESULTS: Overall, 54% received BCS+RT, 23% received mastectomy, and 24% received BCS without RT. The likelihood of mastectomy or BCS without RT was greater for women with increasing age (>80 vs. 66-69) (AOR, 2.48; 95%CI, 2.26-2.73) and (AOR, 3.19; 95%CI, 2.91-3.50) , stage (II vs. I) (AOR, 3.37; 95%CI, 3.15-3.60) and (AOR, 1.30; 95%CI, 1.21-1.39), comorbidity (>2 vs. 0) (AOR, 1.15; 95%CI, 1.05-1.27) and (AOR, 1.39; 95%CI, 1.27-1.52), and of non-white race vs. white (AOR, 1.30; 95%CI, 1.17-1.44) and (AOR, 1.27; 95%CI, 1.14-1.41). The likelihood of mastectomy or BCS without RT was decreased for those who saw an oncology vs. general surgeon (AOR, 0.73; 95%CI, 0.62-0.85) and (AOR, 0.52; 95%CI, 0.45-0.61), lived in metro areas (AOR, 0.68; 95%CI, 0.62-0.75) and (AOR, 0.72; 95%CI, 0.65-0.79), areas of higher education (AOR, 0.72; 95%CI, 0.67-0.78) and (AOR, 0.78; 95%CI, 0.72-0.84), and higher income (AOR, 0.89; 95%CI, 0.81-0.97) and (AOR, 0.85; 95%CI, 0.78-0.92), than women who received BCS+RT. CONCLUSIONS: Treatment for early-stage BC is associated with socio-demographic characteristics and factors such as stage, surgeon specialty, and comorbidities, perhaps reflecting a notion that RT is not well tolerated among the elderly. Treatment could be improved by ensuring all patients are informed of, have access to, and receive full treatment, unless meeting specific treatment guideline criteria for exemption.