Magnetic resonance imaging (MRI) brain scans were performed on 24 schizophrenic patients, 22 bipolar affective patients, and 25 normal control subjects without medical or psychiatric illness using a Picker Vista 0.5 tesla scanner. Specific callosal regions and the cerebral area on the midsagittal slice were measured utilizing the technique described by Nasrallah et al. (1986). No significant differences were found among diagnostic groups in anterior, mid, or posterior callosal width, callosal area, cerebral area, callosal to cerebral area ratio, or the genu (first quartile) to splenium (fourth quartile) ratio. However, male subjects had a significantly greater callosal and cerebral area than female subjects. Gender differences were shown in the genu to splenium ratio in the control groups, but not the affective or schizophrenic groups. The implications of these gender differences are discussed in relation to other studies.