OBJECTIVE: To estimate the prevalence of fibromyalgia (FM) and to compare some descriptive epidemiological and quality of life data between persons with and without FM criteria in a representative sample of the general Spanish population. METHODS: Cross sectional study of 2,192 Spaniards aged 20 or above, selected by cluster sampling. Subjects were invited to a structured interview carried out by trained rheumatologists to ascertain various musculoskeletal disorders. The visit included screening and examination, validated instruments for measuring function (HAQ) and quality of life (SF-12) and questions about socio-demographic characteristics and musculoskeletal, mental, and other general symptoms. FM was suspected in subjects with widespread pain for more than three months. FM was defined by theAmerican College of Rheumatology classification criteria. All estimates are adjusted to sampling scheme. RESULTS: The prevalence of FM in Spain is 2.4% (95% CI: 1.5-3.2). FM is significantly more frequent in women (4.2%) than in men (0.2%), with an OR for women of 22.5 (95%CI: 7.2- 69.9), mainly in the 40-49 years age interval. It is more frequent in rural (4.1%) than in urban settings (1.7%), with an OR for rural settings of 2.5 (95%CI: 1.03-5.9). FM is associated with a low educational level, to a low social class, and to self-reported depression. The scores in the HAQ and in the SF-12 were significantly lower in FM subjects, despite adjustment by covariates. CONCLUSION: FM has a high prevalence in the general population. FM is associated to female gender, comorbidities, age between 40 and 59 years, and a rural setting. Persons fulfilling FM criteria show impaired functioning and quality of life.