OBJECTIVES: BMT is an important technology used in the treatment of cancer patients. Cost estimates for this procedure vary, and mostly derive from estimates developed early in the dissemination of the technology. Our objective was to describe the costs associated with BMT. METHODS: Using 1999 MarketScan data, we analyzed commercial non-Medicare inpatient claims for patients who underwent initial BMT. Costs are comprised of total gross payments to all providers associated with the admission, including physicians and hospital facilities. RESULTS: 69 patients were eligible for analysis. 42% and 29% of the sample were from the North Central or Southern region of the U.S. Mean age was 44 years. The mean and median total claims paid for BMT were $83,027 and $76,826, respectively (95% CI: $72,520, $93,534). The average length of stay (LOS) was 25.6 days (95% CI: 22.9, 28.4). Average costs increased as LOS increased ($49,501 for LOS 0-15, $74,384 for LOS 16-30, $99,050 for LOS 31-45, and $169,431 for LOS>45). The most frequent diagnoses for the sample were: multiple myeloma 19%, non-Hodgkin's lymphoma 16%, other types of cancer 13%, myeloma 10%, and chronic myeloid leukemia 9%. The average cost of BMT was significantly more expensive for patients with a diagnosis of leukemia (e.g. chronic myeloid leukemia) ($94,473) versus patients with other types of cancer ($72,535) (95% CI for the difference: $1,639, $42,498). Mean costs were higher for patients who died ($111,025) versus those patients discharged to their home, either under self-care ($80,618) or medical supervision ($65,291). CONCLUSIONS: We found that costs for BMT vary by diagnosis, LOS, and patient outcomes. Our estimate for BMT appears to be less expensive than initial estimates ($250,000). However, our analysis only included costs for initial BMT whereas other cost estimates include additional costs, such as costs for rehospitalizations, follow-up care and outpatient medications.