Gentamicin- and methicillin-resistant strains of Staphylococcus aureus have been isolated from Spring 1979 to the present from many hospitals in New York City. A large proportion of the strains were resistant to the majority of antistaphylococcal antibiotics. The ratio of multiply resistant strains was highest among tetracycline-resistant strains. There were significant differences in phage susceptibility patterns and the resistance spectrum of strains isolated at different hospitals, whereas strains isolated at the same hospital often showed a marked degree of similarity. This suggests multiple origins of gentamicin- and methicillin-resistant strains isolated in New York City.