We conducted a retrospective study of 50 patients with West syndrome who had been treated with ACTH. The patients were classified into two groups; group I, receiving standard dose of ACTH (0.025 mg/kg/day); and group II, receiving low dose of ACTH (0.015 mg/kg/day). The short-term effect of treatment was evaluated. Each group was further divided into two subgroups; cryptogenic (I-C, II-C) and symptomatic (I-S, II-S). There was no significant difference in the control rate of clinical seizures, between the two dosage groups of cryptogenic etiology. In the symptomatic cases, a greater effectiveness was achieved in group II-S than I-S. None of the patients with cryptogenic etiology experienced any relapse of infantile spasms. Patients with symptomatic etiology had a higher incidence of relapse. The rate of clinical and EEG seizure control was lower, and the incidence of side effects was higher in group I-S patients. The poor short-term effect of treatment in group I-S patients may be due to a higher incidence of prenatal etiology.