Because there are both treatable and untreatable causes of dementia, the physician's ability to conduct (or refer a patient for) a differential diagnosis could have a profound effect on health outcomes for patients and on health care costs. This study was undertaken to assess physician practices with regard to the diagnosis of dementing disorders. Data from 53 physicians (a response rate of 48%) in several specialties were obtained from a self-administered mail questionnaire. Results indicate that the majority of physicians provided history taking, physical examination, and neurological examination. Physicians were more likely to refer patients for psychiatric and neuropsychological examinations than to provide these services themselves. The results also point to deficiencies in two key areas: the use of formal, published diagnostic criteria, and the use of mental status and cognitive function tests. Over 75% of physicians surveyed did not use either DSM-III or NINCDS-ADRDA diagnostic criteria, and 42% of physicians did not provide any mental status tests themselves. The need for continuing education to close knowledge gaps is emphasized.