Both in Japan and the United States, there is an emerging recognition of Kawasaki syndrome pedigrees with multiple affected members. This study reports on 18 families with multiple affected members. Occurrence in siblings represented 0.5% of children with Kawasaki syndrome in San Diego, Calif, and Boston, Mass. There were also 9 more complex pedigrees with 24 affected children. In these complex pedigrees, the onset of the disease was separated temporally and often geographically as well. No clear pattern of inheritance emerged. Given the existence of sibling cases and complex family pedigrees, physicians should counsel affected families and make them aware of the possible increased risk of Kawasaki syndrome among first-degree relatives.