A case of complex partial seizures evolving into periodic spasms is described. A six-month-old boy was referred to us because of complex partial seizures characterized by impairment of consciousness followed by adversion of the eyes and face associated with asymmetric tonic neck reflex-like postures. Interictal electroencephalography (EEG) on admission revealed multiple independent spike foci and clusters of the fast activities, which tended to be pseudoperiodic, during sleep. Ictal EEG showed irregular high voltage slow waves in the left hemisphere which gradually developed into diffuse slow waves followed by periodic sharp and/or slow waves associated with periodic spasms every two or five seconds. He had mild hemiparesis in the right upper limb. Otherwise his development of gross movement was normal. His seizures occurred frequently during the waking state, but sodium valproate was effective. In West syndrome, it is well known that epileptic seizures are characterized by a series of spasms. However, few patients with partial seizures in infancy have been reported to have periodic spasms