We investigated the epidemiology and clinical features of invasive S. pyogenes infection in a pediatric population over a 7-year period (1984-90) by retrospective review. An increasing frequency in invasive infections had occurred (0-11.81/10,000 admissions). A large proportion (48%) of these were orthopedic infections. An epidemic strain was typed as M1T1. This increase appears to have occurred in the context of an overall increase in S. pyogenes infections ("scarlet fever" 1.47-11.22/10,000 outpatients; "strep throat" 4.41-46.54/10,000 outpatients).