['To estimate the cost-effectiveness of an adjuvant treatment course of spa treatment compared with usual care only in patients with fibromyalgia syndrome (FM).', '134 patients with FM, selected from a rheumatology outpatient department and from members of the Dutch FM patient association were randomly assigned to a 2(1/2) week spa treatment course in Tunisia or to usual care only. Results are expressed as quality-adjusted life years (QALYs) for a 6-month as well as a 12-month time horizon. Utilities were derived form the Short Form 6D (SF-6D) scores and the visual analogue scale (VAS) rating general health. Costs were reported from societal perspective. Mean incremental cost per patient and the incremental cost utility ratio (ICER) were calculated; 95% confidence intervals (CIs) were estimated using double-sided bootstrapping.', 'The data of 128 (55 spa and 73 controls) of the 134 patients (96%) could be used for analysis. Improvement in general health was found in the spa group until 6 months of follow-up by both the SF-6D (AUC 0.32 vs 0.30, P < 0.05) and the VAS (AUC 0.23 vs 0.19, P < 0.01). After 1yr no significant between-group differences were found. Mean incremental cost of spa treatment was 1311 Euro per patient (95% CI 369-2439), equalling the cost of the intervention (thalassotherapy including airfare and lodging), or 885 Euro per patient based on a more realistic cost estimate.'] Is cost-effectiveness of Spa treatment for fibromyalgia : general health improvement for free?