We evaluated the clinical features of 32 patients with pulmonary infections caused by methicillin-resistant Staphylococcus aureus (MRSA). Most of the patients were elderly, postoperative, and had severe underlying diseases. Chest radiograph typically showed bilateral and multilobar involvement. Empyema was not common and no abscess was identified. Mortality rate was 38 percent. We also performed an epidemiologic study of MRSA infections by chromosomal DNA analysis using pulsed-field gel electrophoresis. Thirty-two strains were classified into 20 different types by chromosomal DNA pattern, and 5 epidemic strains were observed. These strains were considered to be transmitted among patients by hospital personnel.