Background : In Korea, the rational use of antibiotics are rarely controlled, and their patterns of utilization are not understood. In order to reduce the excessive use and to improve the appropriate use of antibiotics, it is necessary to accurately determine present uses of antibiotics in hospitals. Methods : Analysis of the use of prescription drugs was performed on NFMI(National Federation of Medical Insurance) 1994 medical expense claim data. A stratified sampling by types of hospitals, departments, and diseases was obtained from 1994 August data. Patients with secondary diseases were excluded. In this study, 2,697 adults with URI, 6,397 children with URI, 704 adults with bronchitis, and 1,838 children with bronchitis were included. Results : Most patients were prescribed medication (95.2-99.6%). Of the patients prescribed medication, more than 85% of URI patients and more than 91% of bronchitis patients were prescribed antibiotics. Antibiotics expenses accounted for 14% of total medical expenses in adults and 9% of total medical expenses in children. In adults with URI, antibiotics expenses accounted for 52% of drug expenses. Of the patients prescribed antibiotics, average number of antibiotics used was 1.6-1.7. For patients who are prescribed antibiotics, drug expenses were 62-97% greater than patients not prescribed antibiotics. When children were prescribed antibiotics, the highest price of drugs prescribed were 3.4-fold greater. In addition, the number of drugs prescribed also increased by more than one. Elderly patients, more than 60 years, were prescribed antibiotics less frequently. Children less than 10 years and elderly patients greater than 60 years old were prescribed fewer antibiotics than other patients. And they were prescribed medications for longer days than other patients. Conclusion : This study demonstrated that the average rate of prescribing antibiotics was higher in Korea than other countries. Measures to reduce overuse of antibiotics and to improve the appropriate prescription of antibiotics must be considered for cost effective treatment and overall health of people.