The epidemiology of Kawasaki disease in the six-county Chicago metropolitan area (total population, greater than 7,100,000 inhabitants) was characterized by identifying cases, with onset occurring from 1979 to 1983, inclusively, that had been studied by echocardiography. A retrospective survey of the records from pediatric echocardiographic laboratories and pediatric cardiologists at teaching hospitals, as well as a random sample survey of nonteaching hospitals with pediatric beds in the metropolitan area, was carried out. A total of 190 cases were identified, yielding an annual mean minimum incidence of 5.95 per 100,000 children less than 5 years old. Cases occurred endemically with superimposed spring clusters in 1980 and 1983. As seen in other studies, the male-female ratio was 1.58:1, and the peak incidence occurred in children between 1 and 2 years old, with 85% of cases occurring in children under 5 years of age. The racial distribution of cases was as follows: whites, including Hispanics, 62%; blacks, 32%; Asians, 5%; and half-white/half-Asian, 1%. Asians were slightly overrepresented in that they made up only 1.7% of the study area population. The annual minimum incidence for Asian Americans was 24.4 per 100,000 children less than 5 years old; this rate was significantly greater than those for the other racial groups. Although few cases were observed in Japanese-American children, the calculated annual minimum incidence in this small group was approximately 44 per 100,000 children less than 5 years old. The highest incidence was observed in several suburban Chicago zip code areas, where annual rates as high as 84.7 per 100,000 children less than 5 years old were documented. Coronary artery abnormalities were diagnosed by echocardiography in 30 (16%) of 190 cases; the male-female ratio of patients with such abnormalities was 2.75:1. Whites and children under 1 year of age demonstrated the highest incidence of coronary artery abnormalities. White children under 1 year of age appeared to be at particularly high risk for development of coronary abnormalities, with 11 (41%) of 27 white infants manifesting such findings by echocardiography. These infants may represent a subgroup of patients who would benefit particularly from therapy with intravenous gamma globulin for prevention of coronary abnormalities and who require particularly close follow-up care.