This study aimed to evaluate the patterns of inappropriate medication use and inappropriate dosage in elderly patients in Korea. A retrospective study was performed for the elderly 65 years or older admitted from January 2007 to December 2007 in a medical center, Seoul, Korea. Potentially inappropriate medication (PIM) use in the elderly was evaluated using Beers criteria. Eighteen drugs out of Beers criteria were included in the formulary of the institute. Inappropriate dosage was set using Beers criteria, CMS (the Centers for Medicare& Medicaid Services) guideline, Geriatric Dosage Handbook. As results, the patients with PIM were 2,172 during the study period. The commonly used inappropriate medications were drugs for the nervous system (n=1237, 44.78%), the alimentary System (n=663, 24.54%) and the cardiovascular system (n=494, 18.28%). The elderly patients with prescription of inappropriate dosage were 10% out of patients with PIMs. The commonly inappropriate dosage drugs were digoxin (n=75, 27.27%), diazepam (n=70, 22.55%) and ferrous sulfate (n=66, 24.00%). Logistic regression analysis showed the number of PIM, days of hospital stay as predictors related to inappropriate dosage use. In conclusion, CNS drugs were frequently prescribed as PIM and inappropriate dosages were identified. It is needed to develop a means of decreasing adverse drug events in elderly.