Overuse of antimicrobial agents occurs globally in both community and hospital settings. Misuse of antibiotics can lead to a variety of adverse outcomes, including the development of antimicrobial resistanceand increased cost of hospitalization. This issuehas been particularly problematic in developing countries, where antibiotic-management programs rarely exist and where antibiotics can be purchased without aprescription. In Thailand, the rate of antibiotic resistance among gram-positive and gram-negative or-ganisms has increased significantly over the past decade. These findings provide compelling evidence ofthe need for more-rational use of antimicrobial agents in Thailand. Clinical Infectious Diseases2006; 42:768–752006 by the Infectious Diseases Society of America.