The Korean population is aging rapidly. In 2004 the proportion of 65 years or over is 8.7% of all population, but they consume about 20% of medical resources. The majority of them are suffering from multiple chronic disorders and necessarily polypharmacy, which can result in various adverse drug reactions in elderly patients. Polypharmacy, use of supplements, adherence issues, and the potential for adverse drug events all pose challenges to effective prescription. Understanding the interplay between aging physiology, chronic diseases, and drugs will help the physician avoid potential adverse drug events as well as drug-drug and drug-disease interactions. In daily practice, physicians should be alert to identify any adverse drug reactions and to find strategies for appropriate prescriptions for the elderly patients. These efforts will help ensure high-quality care for the elderly by preventing iatrogenic disorders, and improve overall health, and finally good quality of life for the aged.