OBJECTIVE To review the premorbid histories of 23 children meeting DSM-III-R criteria for schizophrenia with onset before age 12 years and to compare these with childhood data of later-onset schizophrenics. METHODS Premorbid features up to 1 year before onset of first psychotic symptoms were rated from hospital and clinic records, clinical interviews, rating scales, and tests. RESULTS In keeping with previous studies, specific developmental disabilities and transient early symptoms of autism, particularly motor stereotypies, were common. Comparison with the childhood of later-onset schizophrenics showed greater delay in language development, and more premorbid speech and language disorders, learning disorders, and disruptive behavior disorders. (Sixty percent had received or were estimated to meet criteria for one or more clinical diagnoses.) CONCLUSIONS Childhood-onset schizophrenia may represent a more malignant form of the disorder, although selection and ascertainment bias cannot be ruled out. The presence of prepsychotic language difficulties focuses attention on the importance of early temporal and frontal lobe development; early transient motor stereotypies suggest developmental basal ganglia abnormalities and extend previous findings seen in the childhood of later-onset patients.