OBJECTIVES: To estimate the costs savings in outpatient medical resource use associated with diagnosing fibromyalgia during the four years after fibromyalgia diagnosis, METHODS: A French expert panel, involving 33 general practitioners (GPs) and 27 rheumatologists, was questioned in 2007 by means of a questionnaire describing the UK prescriptions registered in the General Practice Research Database between January 1998 and March 2003 (2260 fibromyalgia patients). Participating experts were asked to describe their clinical practice compared to the UK prescriptions in terms of diagnostic tests, drugs, consultations and referrals. over a period of 4 years before diagnosis to 4 years -plus after diagnosis using one year intervals. Poisson loglinear regression models, published for the UK, allowed to estimate the medical resources consumed if no diagnosis had been established. The impact of diagnosis was evaluated for each of these medical resources. Costs were calculated by multiplying resource use with corresponding French unit costs (€; 2007; both public health care payer perspective and societal perspective including patient co-payments).RESULTS: This study confirms previously published results for the UK: whereas costs gradually increase before diagnosis, a stagnation in costs increase occurs in the year after diagnosis, subsequently followed by a moderate decrease afterwards. The same trend was observed whether the panel consisted of GP or rheumatologists. The savings made as a result of fibromyalgia diagnosis add up to €126 per patient and per year in France from the health care system perspective and €184 from a societal perspective. GP visits, diagnostic tests, drugs and referrals to specialists represent respectively 57%, 23%, 12% and 8% of these savings. CONCLUSIONS: Compared to a diagnosed fibromyalgia patient, a not diagnosed patient represents an incremental cost of €126 from the public health care payer perspective, mainly due to medical nomadism and multiplication of investigations and prescriptions.