Peak age of occurrence in the United States is between 18 and 24 months. Fifty percent of patients are younger than 2 years of age, and 80% are younger than 5 years of age; children older than 8 years of age less commonly develop the disease. In children younger than 6 months of age, the diagnosis often is delayed, because the symptom complex of Kawasaki disease is incomplete. The prevalence of coronary artery abnormalities is higher when diagnosis and Treatment are delayed beyond the 10th day of illness. The male-to-female ratio is approximately 1.5:1. In the United States, 3000 to 5000 cases are estimated to occur each year; the incidence is highest in those of Asian background. Kawasaki disease first was described in Japan, where a pattern of endemic occurrence with superimposed epidemic outbreaks was recognized. A similar pattern of steady or increasing endemic disease with occasional sharply defined community-wide epidemics has been recognized in North America and Hawaii. Clusters generally occur during winter and spring. No evidence indicates person-to-person or common-source spread, although the incidence is slightly higher in siblings of children with the disease.

The incubation period is unknown.