The EEGs of 13,560 patients have been reviewed in order to determine whether abnormal findings, epileptiform or not, have a hemispheric dominance. We have included outpatients and hospitalized patients as well. Eight hundred and thirty-five EEGs had generalized abnormal findings, and 414 EEGs had lateralized abnormal findings. The EEGs of 322 patients (77.7%) had a left predominance, and those of 92 patients (22.3%) had a right predominance, of abnormal findings. A strong left predominance has been noted for the epileptiform discharges, i.e. 128 (79%) vs. 34 (21%). These results raise the possibility that the left hemisphere may be more vulnerable to nosological processes.