The sylvian fissure is known to be one of the most asymmetric structures of the human brain. Sylvian fissure length was measured in post-mortem brains of 35 schizophrenic patients and 33 matched non psychiatric control subjects. The schizophrenics showed a significantly reduced length of the left sylvian fissure (-16%, p less than 0.0001) compared to the control subjects, while the right sylvian fissure length was unchanged. Sylvian fissure asymmetry (left/right ratio) was more reduced in male schizophrenics (-24%, p less than 0.001) than in female patients (-16%, p less than 0.03). This finding is consistent with several post-mortem and MRI studies showing left temporal lobe pathology in a significant proportion of patients and may indicate that schizophrenia is a disorder of early neurodevelopment causing impaired cerebral lateralization.