Abstract: Few studies have examined the relationship of insurance status with the presentation and treatment of breast cancer. Using a state cancer registry, we compared tumor presentation and surgical treatments at presentation by insurance status (private insurance, Medicare, Medicaid, or uninsured). Student’s t-test, Chi-square test, and ANOVA were used for comparison. P-values reflect a comparison to insured patients. From 1996 to 2005, there were 6876 cases of invasive breast cancer with either private (n = 3975), Medicare (n = 2592), Medicaid (n = 193), or no insurance (n = 116). The median age (years) at presentation was 55 for private, 76 for Medicare, 54 for Medicaid and 54 for uninsured. The mean and median tumor size (mm) were 18.5 and 15 for private; 20.9 and 15 for Medicare; 24.2 and 18 for Medicaid; and 29.5 and 17 for uninsured, respectively; (p < 0.001 for all). Fewer women with Medicare and Medicaid presented with node negative breast cancers: private, 73.4% node negative; Medicare, 79.5% (p < 0.001); Medicaid, 60.9% (p < 0.001); and uninsured, 58% (p = 0.005). Significantly more uninsured women had no surgical treatment of their breast cancer: 15.5% versus 4.3% for private (p < 0.001). Among women with non-metastatic T1/T2 tumors, 71.5% with private insurance underwent breast-conserving surgery (BCS), compared with 64.2% of Medicare (p < 0.001), 65% of Medicaid (p = 0.097), and 65.4% of uninsured (p = 0.234). The rate of reconstruction following mastectomy was higher for private insurance (36.6%), compared with Medicare (3.8%, p < 0.0001), Medicaid (26.1%, p = 0.31), and uninsured (5.0%, p = 0.0038). The presentation of breast cancer in women with no insurance and Medicaid is significantly worse than those with private insurance. Of concern are the lower proportions of BCS and reconstruction among patients who are uninsured or have Medicaid. Reduction of disparities in breast cancer presentation and treatment may be possible by increasing enrollment of uninsured, program-eligible women in a state-supported screening and treatment program.