BACKGROUND Although multiple sclerosis is considered as an inflammatory demyelinating disease of young adults, nearly 3% of patients manifest it under the age of 16 years. The aim of this study was to highlight the clinical and demographic features of early-onset multiple sclerosis in Isfahan, Iran. METHODS This prospective study concerned multiple sclerosis patients in whom the disease started before the age of 16 years and who were referred to the only clinic of multiple sclerosis in Isfahan from October 1997 through February 2003. All early-onset multiple sclerosis patients underwent magnetic resonance imaging. Magnetic resonance imaging findings were analyzed according to the Barkhof's criteria. All early-onset multiple sclerosis patients were followed for a mean period of 4.7 years. RESULTS Among 1,238 multiple sclerosis patients, 82 early-onset multiple sclerosis patients were identified. The female to male ratio was 4.5:1. The mean age of onset was 14.1 (range: 5 to 16) years. In 53 (65%) patients, the onset was monosymptomatic; in the remaining 29 (35%), it was polysymptomatic. Sixty-four (78%) patients presented a relapsing-remitting course, 14 (17%) had a secondary-progressive and 4 (5%) had a primary-progressive course. At the last evaluation, the expanded disability status scale score was > or =6 in only 8 (10%) patients. According to Barkhof's criteria, the characteristic magnetic resonance imaging findings were observed in 80 (98%) of early-onset multiple sclerosis patients. CONCLUSION In our study, a high rate of childhood multiple sclerosis was observed that may be because of geographical or ethnic differences. Our study also showed that Barkhof's criteria, which is mostly used in adult patients, could be also applied to early-onset multiple sclerosis cases.