OBJECTIVES: To assess the estimated prevalence of possible fibromyalgia sufferers among the general adults population in Portugal using a screening questionnaire, the LFES-SQ developed by White. METHODS: This questionnaire was administrated to a random community sample of 500 persons interviewed by telephone and positive responders to the screening questionnaire were classified as “pain sufferers”. Using a sample of patients coming to Rheumatologist departments we administrated to them the same screening questionnaire and we diagnosed this entire sample to see if they were fibromyalgia sufferers (using the 1990 ACR criteria). Once we had calculated the ratio between patients “positive” to the screening questionnaire and the number of patients really diagnosed with fibromyalgia, we applied this ratio to our population of “pain sufferers” and therefore obtain an estimate of the prevalence of possible fibromyalgia sufferers. It is important to note that we worked on two different populations. RESULTS: In Portugal following the hospital survey the results were the following: 225 interviewed patients (191 women, 34 men) among them 154 were screened positive (136 and 18) and 51 cases of fibromyalgia (50 and 1) therefore multiplication factors of possible fibromyalgia patients VS number of positive = Total fibromyalgia cases in Lisboa / Number of Patients screened positive i.e . multiplication factor for the total population = 51/154 = 0.331; for women = 50/136 = 0.368 and for men = 1/18 = 0.056. Once those ratio were applied to our random community representative sample of 500 persons we obtained the following : an estimated prevalence of FMS in Portugal of 6.09% of the total population, 8.76% of women and 0.69% of men. CONCLUSION: Those data are higher than the ones obtained in the White study or in the published prevalence of fibromyalgia in the literature, but they allow us to assess an estimated prevalence of fibromyalgia.