Background and Purpose Multiple sclerosis (MS) is an autoimmune disease characterized by inflammatory demyelination. Recent studies have shown that long-term exposure to air pollutants (including PM10 particulates) is potentially an environmental risk factor for MS. We aimed to determine the prevalence rates of MS in two cities with different levels of air pollution.& para;& para;Methods This door-to-door population-based study was conducted between April 2014 and June 2015. Two cities were screened for the prevalence rates of MS: 1) Karabuk, which borders an iron-and-steel factory, and 2) Akcakoca, which is a coastal city located in the same region. A validated survey form was used for screening MS. The 2010 McDonald Criteria were used for diagnosing MS. The patients were examined twice, first by a neurology assistant in the field and then by a senior neurologist in public health centers in the cities.& para;& para;Results The prevalence of MS was 95.9/100,000 in Karabuk and 46.1/100,000 in Akcakoca. In total, 33 patients were diagnosed with clinically definite MS. The female/male ratio was 1.5, and 21 patients were diagnosed with relapsing-remitting MS, 9 with secondary progressive MS, and 3 with primary progressive MS.& para;& para;Conclusions We found that the prevalence of MS was more than two fold higher in Karabuk than in Akcakoca, which supports a link between air pollution and the pathogenesis of MS. However, larger etiological and epidemiological studies are needed to confirm this hypothesis.