Two hundred and twenty-eight cases of children with final clinical diagnoses of childhood psychosis were reviewed using a standard coding scheme; cases were grouped in three broad categories on the basis of clinical diagnosis (autistic, atypical and schizophreniform). These three groups differed significantly in many respects, although the 'atypical' group more closely resembled the autistic group. While it was possible meaningfully to differentiate diagnostic groups using DSM-III criteria, some cases were difficult to classify. Childhood schizophrenia, as strictly defined, was far less common than childhood autism. The development of diagnostic schemes for those children whose disorders are difficult to classify is an important topic for future research.