PURPOSE: The purpose of this study was to demonstrate by functional MRI (MRI) the location of the primarymotor cortex in patients with schizencephaly. MATERIALS AND METHODS: fMRI was performed in four patients withschizencephaly who complained of seizures;three were right handed and one was ambidex trous. Associated lesionswere agenesis of the corpus callosum in one patient and absence of the septum pellucidum in another. fMRI employedthe single sliced FLASH BOLD technique using a 1.5-T MR imager with a standard head coil, and was obtained in theaxial plane. Thirty consecutive images were obtained on finger movements of each hand were obtained;the motor taskconsisted of repetitive finger to thumb opposition. Percentage change in primary motor cortex signal intensity wascalculated, and ipsilateral activation index was compared betweenthe affected and unaffected hemispheres. RESULTS: Percentage change in signal intensity increase in the activated area of the unaffected hemisphere ranged from4.8% +/-0.9% to 9.2+/-1.2%(mean:5.6%+/-1.5%) of the baseline value. The ipsilateral activation index of the affectedhemisphere was 0-0.38 and that of the unaffected hemisphere was 15.4-Infinity;in patients with schizencephalysignificantly different(p<0.01). CONCLUSION: Our results suggest that increased activation in the unaffectedhemisphere reflect functional reorganization of the primary motor cortex.