With several US centers reporting up to 40% of strains of S. aureus as MRSA, there is increasing concern about this organism in Canadian healthcare institutions. A retrospective analysis of microbiology records from 1981-88 at The Toronto General Hospital and from 1989-95 at The Toronto Hospital (Western and General Divisions) reveals an incidence of MRSA which has varied between 0.6-2.3% of all S. aureus isolates. The rate of MRSA isolation has varied between 3-11/10,000 admissions with the peak of 11/10,000 admissions and 2.3% of all isolates noted during a small outbreak in 1982-83. Respiratory tract isolation accounted for 84-86% of MRSA isolates in 1982-83 but only 30-48% of isolates in 1993-1994. Two clusters of MRSA have been identified, one in 1982-83 and the other in 1991-92 which was a Staphaurex^TM negative strain. Epidemiologic data and genotypic analysis using pulsed-field gel electrophoresis (PFGE) implicated a specific strain associated with nasal carriage by medical staff in the 1982-83 cluster and probable cross-contamination between patients in the 1991-92 cluster. Whereas 88% of the MRSA isolates in 1982-83 were considered nosocomial, approximately 32% (p<0.001) were considered nosocomial in 1994-95 reflecting a higher proportion of patients colonized on admission or on transfer. Our experience with a strict isolation policy and an aggressive approach towards suspected MRSA over 15 years suggests that nosocomial transmission of MRSA can ve controlled within a large tertiary Canadian healthcare institution.