From 1974 through 1991, a total of 583 children with Kawasaki disease were seen at the Hospital for Sick Children, in Toronto, of whom 80 (13.7%) had coronary artery involvement. There were 55 boys and 25 girls, whose mean age at onset was 2.9±2.5 years, followed for a mean period of 4.0±3.6 years. Giant aneurysms (maximum diameter ≥8 mm) were found in 22 children, moderate-sized aneurysms (≥4 to <8 mm) in 44, and dilation lesions (<4 mm) in 14. Myocardial infarction occurred in 9 (1.5%), all of whom had giant aneurysms. The persistence rate for aneurysms was 72% at 1 year and 41% at 5 years of follow-up. In multivariate analysis, the regression of an aneurysm was significantly related to the severity of coronary artery lesions, initial treatment, and gender. Although >80% of small or moderate-sized aneurysms regressed within 5 years, giant aneurysms did not regress during the follow-up period. In patients who received immune globulin therapy, coronary lesions tended to resolve more rapidly than in those treated with salicylate therapy alone, because 91% of the lesions in the former were small or moderate. These findings suggest that the severity of coronary artery involvement during the initial stages of Kawasaki disease influences the regression of these lesions, and that immune globulin treatment may improve outcome by reducing the incidence of severe lesions.