OBJECTIVES The occurrence of breast cancer causes significant morbidity and mortality among patients and results in considerable economic impact on patients, health care payers, and society. The purpose of this study is to determine the trends in the prevalence of breast cancer and associated health care utilization and costs among an indigent population covered by a state Medicaid program. METHODS Retrospective analysis of a state Medicaid fee-for-service administrative claims dataset for each calendar year from January 1, 2000 to December 31, 2005 was performed. Breast cancer prevalence was determined based on the number of females (21-64 years) having at least one medical services claim with a primary diagnosis of breast cancer (ICD-9-CM codes 174, 233.0x, 238.3x, or 239.3x) at any time during the calendar year. Corresponding medical services use and patterns of treatment were also reported among females with breast cancer for each year. State Medicaid perspective was used to calculate costs (2005 US dollars). RESULTS From 2000 to 2005, the number of female recipients with breast cancer increased from 789 to 1205, respectively. Female recipients in the age group 45-64 years represented the highest proportion in all the study years, increasing from 78.6% in 2000 to 83.9% in 2005. Consistent with state population demographics, a majority (>90%) of recipients in each year were white. Office visits represented a large majority of medical services encounters (>98%) and costs (>90%) in each year. The average amount per recipient paid by Medicaid for breast cancer-related medical services use increased from $2637 to $3570 between 2000 and 2005, respectively. The average cost per office visit increased from $255/visit to $429/visit during the same period. CONCLUSIONS Breast cancer prevalence increased between 2000 and 2005. There has been a substantial increase in the cost impact associated with breast cancer on the State Medicaid program during the same period.