Intellectual functioning of children diagnosed as schizophrenic is systematically reviewed. According to the reports in the literature, over 50% of these children could be classified as having borderline or subnormal intelligence by conventional criteria. On perceptual and motor tests, the performance of the intellectually retarded schizophrenic children was similar to that observed in younger normal children, mentally retarded adults, and adults with severe mental changes as a result of brain disease.Neither childhood schizophrenia nor mental retardation is a distinct clinical entity encompassing homogeneous groups. When severe behavior disorder coexists with intellectual defect in childhood, the altered behavior may be a reflection of cerebral dysfunction. Which aspect is stressed–the retardation or the behavior disorder–is, in part, a function of the observer's orientation rather than the child's behavior.The general disagreement, and the lack of clarity in this field, may be due largely to the paucity of systematic, controlled experimentation.