Iatrogenic diseases are common in the elderly, particularly in the hospitalized patient. Adverse outcomes may be induced by poor communication with patients, inadequate history and examination, and inappropriate use of diagnostic resources. However, even when resources are used appropriately, adverse outcomes do occur, hence the price paid for sophisticated medical and surgical techniques. Medications offer a great potential for adverse reactions, and careful prescribing and knowledge of the pharmacokinetic changes that occur with aging, particularly impaired renal excretion of drugs, together with the use of the minimum number of drugs and maneuvers to improve compliance, can reduce this risk. Complications of surgery should be anticipated and promptly recognized and managed.