We investigated anterior cingulate gyrus (ACG) volume in 40 patients with schizophrenia (20 males, 20 females) and 40 age-and sex-matched normal controls using three-dimensional magnetic resonance imaging (MRI). Volumes of the whole brain and both the gray and white matter of the ACG were measured on consecutive coronal 1-mm slices. There was no significant difference between the patients with schizophrenia and the normal controls in the whole brain volume. Right ACG gray matter volume was significantly reduced in the female patients with schizophrenia as compared with the female controls. Furthermore.in the female controls, ACG gray matter volume was significantly larger on the right than on the left, while this asymmetry was not significant in the female patients. ACG white matter findings were similar to those of the ACG gray matter in that the volume was significantly larger on the right in the female controls, and this normal structural asymmetry was reduced in the female patients. These results suggest that gender may play an important role in the structural asymmetry anomalies in schizophrenia.