Lesion size correlated positively with the severity of apraxia in the acute (one month) and chronic (one year) stage in 177 stroke patients, but accounted for only 25 per cent of the variance of the apraxia scores. Apraxia was measured on a standardized battery and defined in relation to normal controls. Lesions visualized by CT were traced objectively and measured on standard templates. Small lesions (less than one-tenth of the hemispheric volume) producing moderate or severe apraxia were mostly frontal and close to the body of the lateral ventricle. The lesions of the deep parieto- and occipitofrontal and anterior callosal fibres seem to be crucial in apraxia, rather than the parietal cortex as traditionally claimed. Large lesions (more than three-tenths of the hemisphere) without apraxia were associated with atypical asymmetries in half of the cases, as measured by the torque and the width of the frontal and occipital lobes on CT scan, suggesting a right hemisphere role in sparing and recovery of praxis.