We interviewed 315 consecutive elderly patients admitted to an acute care hospital to determine the percentage of elderly hospital admissions due to noncompliance with medication regimens or adverse drug reactions, their causes, consequences, and predictors. Eighty-nine of the elderly admissions (28.2%) were drug related, 36 due to noncompliance (11.4%), and 53 due to adverse drug reactions (16.8%). One hundred three patients had a history of noncompliance (32.7%). Factors statistically associated with a higher risk of hospitalization due to noncompliance were poor recall of medication regimen, seeing numerous physicians, female, medium income category, use of numerous medications, and having the opinion that medications are expensive. Factors associated with an increased risk of an admission due to an adverse drug reaction were use of numerous different medications, higher medication costs, receiving Medicaid, and not receiving any home services. In conclusion, many elderly admissions are drug related; noncompliance accounting for a substantial fraction of these. Elders at high risk of being noncompliant are identifiable using a variety of criteria. Economic factors were important in predicting admissions due to noncompliance as well as adverse drug reactions.