Pathomorphology of the limbic system has been described in post-mortem studies of schizophrenia. To determine whether this could be detected in living patients and was not secondary to the treatment or the chronicity of the disease itself, we measured the volumes of the hippocampus-amygdala complex and adjoining temporal horns of 34 patients in their first episode of schizophrenia and 25 normal volunteers using T1 weighted contiguous coronal magnetic resonance images of 3.1 mm width. The results demonstrate abnormal medial temporal lobe morphology in a subgroup of patients at the onset of their illness. There were clear laterality effects and sex differences: hippocampal tissue was significantly smaller only in the left hemisphere of male patients, whereas enlargement of the whole temporal horn or its anterior portion was present on the left side in both sexes. Dysfunction of the limbic mesiotemporal structures might explain some of the clinical features of the disease.