Cerebral glucose metabolism of 18 patients with multi-infarct dementia (MID) and 10 age-matched normal subjects were examined with positron emission tomography and the 18-F-fluoro-deoxy-glucose technique. MID patients had significantly lower glucose metabolism in all the grey matter regions measured and were also characterized by more individuality in metabolic pattern. MID patients were also evaluated as to intelligence quotient (IQ). A positive correlation between IQ as shown by the Tanaka-Binet test and glucose metabolism for the entire grey matter was found. The clinical applicability of this test for predicting cerebral metabolism is discussed.