The effect of insurance payer status on surgical treatment of early stage breast cancer is unclear. This retrospective study examined the effect of insurance payer on mastectomy rates of 1539 women treated within a single health system. Women with Medicaid had significantly larger tumors compared with those with private insurance (PI) at diagnosis (3.3 cm vs 2.1 cm, P < .05) and were more likely to be treated with mastectomy for larger tumors compared with women with PI. However, women with PI were more likely to have mastectomy for smaller tumors; among women with tumors less than 2 cm, 11% with Medicaid underwent mastectomy compared with 47% with PI (P < .05). Overall, when compared with those with PI, women with Medicaid were more likely to receive mastectomy (60% vs 39%, P < .05).