Sixty-one cases of Kawasaki syndrome (KS) occurred in Harris County, Texas, during the three-year period from January 1982 through December 1984. Fifty-five (90%) of these 61 patients were under 5 years old, for an annual endemic rate in children under 5 years old of 9.1 cases per 100,000 per year. To our knowledge this is the highest endemic rate reported to date in the continental United States. Between Aug 26 and Sept 19, 1984, seven children with KS were hospitalized in Harris County. The seven children were between 5 months and 5 years old. The number of cases in this cluster was unusual for late summer, which is generally a low-incidence season for KS in Harris County. More important, a case-control study of these children revealed that they resided significantly closer to a bayou or drainage ditch than did randomly selected matched control subjects. A similar association with drainage ditches or creeks was observed in a subsequent cluster of 13 cases of KS in seven eastern North Carolina counties. To our knowledge, this is the first report of a possible association between KS and residing near water.