Previous studies have demonstrated the efficacy of intravenous gamma globulin in the prevention of coronary artery abnormalities in Kawasaki disease. We retrospectively reviewed our single-hospital experience with patients in whom Kawasaki disease was diagnosed from January 1979 to July 1987. Only 3 of 68 (4%) patients treated with intravenous gamma globulin in the first 10 days of illness developed coronary artery abnormalities (one of the three had abnormalities before gamma globulin therapy), in comparison with 39 of 119 (33%) patients not treated with gamma globulin (p less than 0.001). Giant coronary artery aneurysms, which are associated with the greatest morbidity and mortality rates in Kawasaki disease, developed in none of the 68 patients treated with gamma globulin but in 7 of 119 patients (6%) not treated with gamma globulin (p = 0.04). Intravenous gamma globulin appears to be effective not only in reducing the overall prevalence of coronary artery abnormalities in Kawasaki disease but, more important, in preventing the formation of giant aneurysms, the most serious form of coronary abnormality after this illness.