Objectives: To determine the prevalence of Thai demyelinating diseases regarding demographic data, symptoms and signs, associated diseases, disease progression, cerebrospinal fluid analysis and imaging findings. Methods: A multicenter retrospective study of 107 MS patients attending the Neurological Centers in Thailand during June and December 2004 was performed. Each had an initial diagnosis of demyelinating diseases. Results: From 107 patients, there were 78.5% female and 21.5% male with the female: male ratio of 3.7:1. The age at onset was 32.7±11.5 years. The mean disease duration was 3.8±5.1 years and the mean number of relapses was 4.6±4.4 with annual relapse rate of 1.5±1.3 times. None reported a family history of MS. Recurrent optico-spinal form was 27.1% followed by 17.8% of spinal form and 15% of western form of MS. The most common presenting symptom was visual impairment (51.4%). Only 24.1% demonstrated oligoclonal bands in CSF. The median score of EDSS at their latest visits was 3.0 with mean score of 3.8±3.0. Conclusions: MS in Thailand is different from Western countries. There were no occurrence of MS in families, higher incidence of visual impairment at onset, more common recurrent optico-spinal form and lower incidence of oligoclonal bands in the CSF.