OBJECTIVES: CML has a worldwide incidence between 1 and 2 per 100,000 and accounts for 15% of all leukemia patients. In the US, the total 2004 hospitalization costs for CML patients was estimated at $69 million. However, beyond that figure, little information is available on costs of other resources for treating CML patients or how the costs vary with severity of illness. The objective was to estimate the costs of treating CML and the unintended effects of treatment according to disease phase, response type to treatment, and time since diagnosis (0 to 3, 4 to 12 and >12 months). METHODS: Using a questionnaire based on current treatment guidelines, we elicited the expert opinion of five oncologists and the frequency of resource use in: outpatient visits, laboratory tests and other interventions. Costs were obtained from publicly available sources and are presented in 2006 USD. RESULTS: In the first three months of each phase, a patient responding to treatment was estimated to cost: $744 (low: $325, high: $2654) in chronic phase, $983 ($420, $4119) in accelerated phase, and $5979 ($442, $21047) in blast phase. A patient not responding to treatment was estimated to cost $1002 ($478, $3407) in chronic phase, $1427 ($773, $6617) in accelerated phase, and $10496 ($876, $34471) in blast phase. Costs were higher for patients not responding to treatment, increased as patients progressed through the disease phases of CML and decreased with longer time in the phase. CONCLUSION: Higher costs were associated with patients not responding to treatment in each phase of CML. Although choice of treatment is determined according to patients' responses, disease progression and time since diagnosis, published cost-effectiveness models do not necessarily incorporate all these parameters. The estimates collected in the current study will serve as reproducibly measured inputs in future models.