Background: The frequency of multiple sclerosis (MS) is still undetermined in Tehran. We conducted this survey to assess the incidence trend and point prevalence of MS on March 20, 2009, in Tehran province, Iran. Methods: Data for patients with a definite diagnosis of MS were obtained from the Iranian MS Society (IMSS). The annual incidence rates were calculated based on year of diagnosis. The prevalence and annual incidence rates were standardized using the WHO (2000–2025) population as a standard. Results: We detected 8,026 definite MS cases that had been registered by the IMSS till the prevalence day. The age- and sex-adjusted incidence rates increased significantly from 0.68/100,000 in 1989 to 2.93/100,000 in 2008 with its peak (4.58) in 2005. On March 20, 2009, we identified 7,896 prevalent cases (5,888 females and 2,008 males) yielding an age-adjusted prevalence rate of 50.57/100,000 (females: 77.24 and males: 25.54). The female-to-male ratio was 3.11 (95% confidence interval: 2.95–3.27). The age-specific prevalence showed a peak in the group aged 35–39 years in females and in that of 40–44 years in males with a mean (±SD) age of 35.48 (±9.9) years for females and 36.98 (±10.5) years for males. Conclusion: Tehran is a high-risk area for MS disease, and the incidence has dramatically increased over the last 20 years.

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