We report seizures induced by adrenocorticotropic hormone (ACTH), which were demonstrated clinically and electro-encephalographically, in a severely handicapped 7-month-old infant with West syndrome due to perinatal hypoxicischemic encephalopathy. Although tonic spasms (original seizures) decreased soon after starting ACTH treatment, new brief tonic seizures, somewhat more slowly motioned than the original tonic spasms, frequently appeared only during sleep after consecutive ACTH injections for 11 days, in place of the tonic spasms seen in the waking state. After discontinuation of ACTH therapy with the last injection on the 16th day, the brief tonic seizures began to decrease and finally disappeared in 8 days. Ictal EEG of new brief tonic seizures revealed diffuse fast spiky wave bursts, 50-150 microV and 10-20 c/s, with a duration of 0.5-4 seconds, which were different from attenuation associated with low voltage rhythmic fast activity corresponding to tonic spasms, the original seizures. Therefore, we considered that the new brief tonic seizures, which appeared only during sleep in the course of ACTH therapy, were ACTH-induced seizures.