OBJECTIVE: The planum temporale is intimately involved in the generation and understanding of language and has been suggested to be a key area affected in schizophrenia. To explore temporal lobe abnormalities in schizophrenia, the authors measured the planum temporale, a normally asymmetric area lying on the superior part of the temporal lobe, in schizophrenic patients. METHOD: High-resolution magnetic resonance imaging (MRI) scans were obtained for 14 right- handed schizophrenic patients and 14 healthy comparison subjects individually matched for age, sex, handedness, race, and parental socioeconomic status. The surface area of the planum temporale was measured by using MRI reconstruction techniques. RESULTS: There was striking reversal of the normal asymmetry (left larger than right) in planum temporale surface area in 13 of the schizophrenic patients but in only two of the comparison subjects. However, Heschl's gyrus (primary sensory cortex), which served as an anatomically contiguous nonheteromodal cortical comparison region, showed no difference between the left and right sides in either group. Severity of thought disorder in the patients was related to asymmetry. CONCLUSIONS: This is a clear demonstration of a reversal of expected symmetry in the brains of right- handed schizophrenic patients, which involves a region of key importance in normal human behavior. The nature of the abnormality strongly suggests that schizophrenia is a neurodevelopmental disorder.