We encountered seven children with symptomatic congenital cytomegalovirus (CMV) infection from 1988 to 1995, of whom two (28.6%) developed typical autistic disorder. Case 1: A boy born at 38 weeks' gestation with a birth weight of 3164 g showed generalized petechiae, hepatosplenomegaly, and positive serum CMV-specific IgM antibodies. He was profoundly deaf, mentally retarded, and exhibited a lack of eye contact, stereotyped repetitive play, and hyperactivity. Case 2: A boy delivered at 39 weeks gestation with a birthweight of 2912 g showed non-progressive dilatation of the lateral ventricles observed postnatally. CMV-specific IgM antibodies were positive and CMV-DNA in the urine was confirmed by PCR. The boy was mentally retarded but not deaf. He showed no interest in people and delayed speech development. Subependymal cysts were detected by cranial ultrasound after birth in both patients. This is the first report describing subependymal cysts and the later development of AD. Cranial magnetic resonance imaging revealed an abnormal intensity area in the periventricular white matter suggestive of disturbed myelination; however, no migration disorders were found in our patients. These findings suggest that the timing of injury to the developing brain by CMV may be in the third trimester in some patients with autistic disorder.