There have been few reports about the frequency of multiple sclerosis (MS) in Spain. We undertook a prevalence study in the province of Teruel, which is served by two hospitals as referral centres for a population of 143,680. We found a total of 46 patients who fulfilled Poser's criteria for clinically definite or probable MS with a prevalence rate of 32/100,000 [95% confidence interval (CI): 22.8-41.3]. The prevalence rates for males and females were 23.5 (95% CI: 12.3-34.7) and 40.6 (95% CI: 25.8-55.4) respectively. We found an incidence rate of 2.2/year per 100,000 in the last 5 years. The sex ratio (females/males) was 1.7. The mean age on prevalence day was 40.6 years (range: 15-76). The clinical course was relapsing-remitting in 82% of patients, progressive in 9% and secondary progressive in the other 9%. The mean EDSS score was 3.73 (range: 1-8.5). Our results confirm the hypothesis that Spain is an area at high risk for MS.