Duration of survival from time of first evaluation was studied in 61 patients with clinically diagnosed Alzheimer's disease (senile dementia of the Alzheimer type [SDAT]) and 34 patients with clinically diagnosed multi-infarct dementia (MID). Duration of survival did not differ significantly between MID and SDAT. However, since MID patients were younger at onset, MID patients had a lower life quotient than SDAT patients. Race, sex, and age at onset were not predictive of survival in SDAT. History of hypertension, elevated systolic blood pressure, lower scores on tests of Block Designs, and Logico-Grammatical Comprehension predicted shorter survival in SDAT. Age at onset and race were not predictive of survival in MID. Male sex, lower educational attainment, as well as low scores on tests of Logico-Grammatical Comprehension, Digit Span, Naming, Verbal Fluency, and receptive vocabulary, predicted shorter survival in MID.