Two hundred three isolates of S. aureus were collected from 140 patients during a 1 year period in our hospital in Minas Gerais, Brazil. Of these patients, 102 acquired the infection in the hospital (nosocomial) and are the subject of this report. Fifty-seven patients had Methicillin-sensitive S. aureus (MSSA) strains identified, and 45 had Methicillin-resistant S. aureus (MRSA) strains. The most common sites of clinical infections by S. aureus were bloodstream (bacteremia), surgical/skin wounds and lung (pneumonia). The patients with MRSA infections were most likely to be in the surgical and clinical wards, but those with MSSA infections were most likely to be in the neonatal and emergency units. By univariate analysis, we found several factors associated with an increased risk of MRSA infections: age, mean preinfections and total duration of hospital stay, use of 3 or more antimicrobials, presence of 3 or more indwelling devices (mainly vascular and urinary catheters). Colonization (67.6% x 27.8%; p<0.05) and multicolonization (89% x 11.0%; p<0.05) were more associated with MRSA infection. Of the total of 203 isolates, 110 MRSA were found to be multiresistant, with 106 showing resistance to 5 or more antibiotics, compared to 15/93 (16%) of the MSSA isolates. The most serious cases and higher colonization rates of MRSA occurred in elderly patients. The presence of nosocomial MRSA is a serious medical problem which requires continued attention to care in the overuse of antibiotics and indwelling devices in hospitals.