Context: The National Breast and Cervical Cancer Early Detection Program has increased access to screening services for low-income females since 1991; however, evaluation information from states implementing the program is sparse. This study evaluates the impact of the Missouri program, Show Me Healthy Women (SMHW), on early detection and treatment cost. Objective: To estimate breast cancer treatment and health care services costs by stage at diagnosis among Missouri's Medicaid beneficiaries and assess the SMHW program impact. Design: Analyzed Missouri Medicaid claims linked with Missouri Cancer Registry data for cases diagnosed 2008-2012 (N = 1388) to obtain unadjusted and incremental costs of female breast cancer treatment and follow-up care at 6, 12, and 24 months following diagnosis. Noncancer controls (N = 3840) were matched on age, race, and disability to determine usual health care cost. Regression analyses estimated the impact of stage at diagnosis on expenditures and incremental cost. Show Me Healthy Women participants were compared with other breast cancer patients on stage at diagnosis. A comparison of SMHW participants to themselves had they not been enrolled in the program was analyzed to determine cost savings. Results: Expenditures increased by stage at diagnosis from in situ to distant with unadjusted cost at 24 months ranging from $50 245 for in situ cancers to $152 431 for distant cancers. Incremental costs increased by stage at diagnosis from 6 months at $7346, $11 859, $21 501, and $20 235 for in situ, localized, regional, and distant breast cancers, respectively, to $9728, $17 056, $38 840, and $44 409 at 24 months. A significantly higher proportion of SMHW participants were diagnosed at an early stage resulting in lower unadjusted expenditures and cost savings. Conclusions: Although breast cancer treatment costs increased by stage at diagnosis, the population screening program's significant impact on early diagnosis resulted in important cost savings over time for Medicaid.