The degree of dementia was examined in relation to findings of automated EEG and cranial CT in 50 demented old patients aged 51 - 86. Slow waves on EEC, and dilated ventricle and atrophied cortex on cranial CT were frequently associated with poor psychological scores. As the degree of dilated ventricle increased, the frequency and amplitude of slow waves increased and the frequency and continuity of ..cap alpha.. waves decreased. Dilated ventricle was more strongly correlated with abnormal EEG findings than atrophied cortex. This was more marked in cases of severer patients. Abnormal EEC findings associated with poor psychological scores were more frequently observed in the group of patients with vascular dementia (VD, n = 30) than the group of patients with senile dementia of Alzheimer type (SDAT, n = 20). Abnormal EEG findings were correlated with poor scores on Hasegawa test in the VD group and with those on Bender Gestalt test in the SDAT group. The degree of dilated ventricle was more correlated with abnormal EEG findings in the SDAT group than the VD group. (Namekawa, K.).