A standardized diagnostic evaluation was performed on 200 consecutive patients over age 60 with suspected dementia. Diagnoses were confirmed by consensus and subsequently by follow up. Over 70% had Alzheimer's type dementia; 31% had more than one illness contributing to the dementia state, with overlap between the two groups. The most common so-called "treatable" illnesses were drug toxicity, hypothyroidism, and other metabolic diseases; 248 other medical diseases were recognized in 124 patients. Improvement occurred in 55 patients (27.5%) and persisted in 28 (14%) for at least a year during follow up, but only 2 patients recovered normal mental function. Our results emphasize the importance of recognizing and treating the multiple illnesses that contribute to dementia in elderly adults. The distribution of illnesses in demented elderly outpatients is different from that reported in younger patients with dementia. Diagnostic strategies and expectations need to be based on data obtained from studies of elderly patients with suspected dementia.