The prevalence of West syndrome in Thailand had not been studied. During January 1997 to December 1999, at the Department of Pediatrics, Ramathibodi Hospital, Bangkok, Thailand, of the total 628 first seen epileptic patients, aged 0-15 years, 31 patients (4.9%) with West syndrome were encountered. Sixteen were males. The mean age at presentation was 9.7 months (range 4-32 months) and at seizure onset was 5.7 months (range 2-11 months). Twenty-two patients had typical spasms, four each had generalized tonic seizures and focal seizures prior to the onset of infantile spasms, and another patient had myoclonic seizures. Nineteen patients were classified as symptomatic. Electroencephalogram revealed hypsarrhythmia in six patients, multifocal independent epileptiform discharges in 24 patients, and focal epileptiform discharges in four patients. Abnormal brain-imaging findings were demonstrated in six of the 11 patients investigated. Vigabatrin was given to 17 patients whereas one patient was given valproate. Others who had been severely retarded were given phenobarbital in combination with benzodiazepine. Six patients were lost to follow-up. Of the remaining patients, the duration of follow-up ranged from 7 to 44 months (mean 28 months). Infantile spasms disappeared in 11 patients, persisted in six patients, and changed to other form in eight patients. The developmental outcome was apparently normal in five, slightly delayed in four, moderately delayed in ten, and severely delayed in eight patients.