OBJECTIVES Fibromyalgia syndrome (FMS) is a chronic disorder defined by widespread musculo-skeletal pain that is often associated with a number of comorbidities including fatigue, sleep disturbance, stiffness and functional limitation. In absence of a specific diagnostic test, FMS is typically difficult to identify, and there is limited knowledge about the economic burden of FMS. The objectives of this study were to estimate prevalence of comorbidities, healthcare resources utilization and costs associated with FMS. METHODS A retrospective cohort study was conducted using data from the Quebec provincial health plan (RAMQ) for a random sample of patients with two or more recorded diagnoses of FMS and a control cohort without FMS, matched for age and gender, for a period spanning from June 2006 to July 2007. Prevalence of comorbidities was estimated and a chronic disease score was calculated. Healthcare resources consumed by FMS and non-FMS patients included visits to physicians, physician's interventions, pain-related medications, non-pain-related medications and hospitalizations. RESULTS A total of 16,010 FMS patients were identified, with a matched number of control patients. The mean age of the study population was 58.8 years and most subjects were women (67.8%). The prevalence of most comorbidities and the chronic disease score were significantly greater in the FMS patients than in control group (3.8 vs. 2.8; p <0.001). Health resources utilization during the study period was significantly greater among FMS patients than non-FMS patients: the annual number of physician visits and interventions was 25.1 for FMS vs. 14.8 for non-FMS patients. The amount paid by the RAMQ was significantly greater for patients with FMS ($4065) compared to patients without FMS ($2766, p<0.001). CONCLUSIONS This analysis of the RAMQ database indicated that comorbidities are highly prevalent in FMS patients, and suggested that the economic burden associated with FMS is substantial.