This experiment was designed to determine whether increasing evidence of generalized developmental delay in early-onset psychosis was apparent at a cortical level in autistic children. Using magnitude of dominant ear advantage as an indicator of relative cerebral dominance, unwarned simple reaction time (RT) to monaural presentation of tones was investigated in matched groups of autistic, retarded, and normal children. Analysis of RTs and relative ear advantage as a function of group membership and chronological age indicated that the autistic children showed significant developmental delay in both RT and the establishment of cerebral dominance compared to the control groups. These results thus provide additional evidence of generalized maturational delay at a cortical level in early-onset psychosis, and suggest that the maturational delay of the autistic children is more extensive than the developmental deficits implied by their intellectual impairment. © 1983 Plenum Publishing Corporation.