BACKGROUND: This study was performed to evaluate the prescribing pattern of beta-lactam antibiotics and the relationship between antimicrobial resistance and antimicrobial use in 5 tertiary care hospitals in Korea. MATERIALS AND METHODS: Data on annual patient-days and annual consumption (defined daily dose (DDD) per 100 patient-days) of beta-lactam antibiotics from 2003 to 2005 in 5 tertiary hospitals were analyzed. To determine the antimicrobial resistance in K. pneumoniae, broth microdilution test and double disk synergy were performed according to the CLSI performance standards. Spearman's correlation coeffient was used to determine the relationship between antibiotic consumption and resistance. RESULTS: The prescription of beta-lactam antibiotics in 5 tertiary hospitals markedly varied. In two hospitals, increase in consumption of beta-lactam antibiotics was more than 30% during recent 3 years. The higher consumption of beta-lactam antibiotics significantly correlated with the higher rate of antibiotic-resistant K. pneumoniae in 5 tertiary care hospitals. CONCLUSION: Continuous surveillance of antibiotic use is needed to encourage appropriate prescribing of antibiotics and to reduce antibiotic resistance.