OBJECTIVES: Compare modified Delphi-panel survey methodology with a chart review study on resource data collection and costing. METHODS: Results from a published chart review on the cost of treatment of multiple myeloma in Sweden 2001 – 2005 is compared with a modified Delphi-panel (2008) set up in accordance to Evans et al. (1997, 2000). The panel consisted of four responding haematologists at different university hospital clinics. Costs in year 2008 prices. RESULTS: Background patient characteristics differences between the chart review and Delphi-panel were; gender: 3%, share aged above 65: -28%, mean number of co-morbidities at diagnose: -6%, clinical trial participation: 383%. As expected, the treatment regimen options in 2008 had changed considerably since the chart review with the introduction of thalidomide, bortezomib and lenalidomide, resulting in chemotherapy drugs representing the single greatest increase with Euro1164 (1013%). Consistent with the lower mean age in the Delphi-panel (68 vs. 76) stem cell transplantation showed an increase with Euro698 (303%) and blood cell enhancing drugs with Euro471 (682%). Given the patient characteristics, we saw an expected moderate increase in costs for outpatient visits, laboratory- and diagnostic tests. Mean total cost per patient-month was estimated to Euro4800 in the Delphi panel, or 59% higher than in the chart review. CONCLUSIONS: In therapeutic areas where treatment practice is undergoing rapid changes and treatment guidelines are well accepted and complied with, expert opinions can be a valuable source to capture changes from a well-defined but outdated baseline. However, the recruitment of representative respondents is important to avoid bias in patient selection and treatment practice. We believe our Delphi panel estimation of health care resource utilisation captures the development of MM-treatment in Sweden since the results were in line with our expectations on cost item development compared to the chart review given the patient characteristics.