Magnetic resonance imaging (MRI) scans were used to examine the size and asymmetry of the planum temporale (PT) in 20 schizophrenic patients and 12 strictly matched healthy volunteers. PT lengths from coronal sections were measured and then summed to obtain an estimate of their areas. Schizophrenics showed the lack of the physiological PT area asymmetry evidenced in the control sample and a statistically significant diagnosis by side interaction was observed (F = 4.96; p less than 0.05). The study of PT asymmetry could permit us to better analyse the role of laterality in the pathophysiology of schizophrenia.