OBJECTIVES: To render information on the accuracy of patient-reported indirect cost data. By comparing questionnaire-derived data to payer-derived data on a patient-by-patient basis disease related productivity losses in rheumatoid arthritis (RA) are being validated. METHODS: The assessment of indirect cost data was part of a clinical multicenter randomized RA-trial in Germany. For 234 RA-patients at working age (1987 ACR criteria, membership in the regional statutory health insurance plan, mean age 53 (±9) years, mean disease duration 8 (±7) years, 76% females) every three months corresponding indirect cost data were derived from (i) a health economic questionnaire for cost assessment in patients with RA and (ii) the payer’s database (insurance and physicians’ association) over a period of 18 months. Comparative statistical analyses were performed between patient reported and insurance claims data. RESULTS: The mean annual productivity losses due to sick leave amounted to 14 and 17 days per patient (questionnaire versus payer data), productivity losses due to work disability to 3 days (both); monetary valuation renders overall costs of 1240€ and 1590€, respectively. The difference of 17% in overall productivity losses is not significant. Comparison of productivity losses reveals a strong correlation of r=0.83 in those due to sick leave and of kappa=0.84 in those due to work disability between questionnaire and payer data. CONCLUSIONS: The comparison of questionnaire and payer data shows that RA-patients report their productivity losses adequately. Indirect cost assessment should therefore be included in further RA-trials and observational studies, even if payer-derived data is not available.