The authors conducted a retrospective hospital-based chart review of cases of hemolytic-uremic syndrome among children less than or equal to 18 years of age, hospitalized in Oregon during the four-year period from January 1979 to December 1982. Thirty children with hemolytic-uremic syndrome living in Oregon were hospitalized during this period, for an average annual incidence of 0.97 cases per 100,000 children. Seventy per cent of cases occurred in children under five years of age, for an incidence of 2.65 cases per 100,000 children. Twenty-seven (90%) of the 30 children were white, and 17 (57%) were female. Twenty-four (80%) had a diarrheal prodromal illness including 20 who had bloody diarrhea. Twelve children (40%) acutely required peritoneal dialysis, and two (7%) developed chronic renal failure. Three children died, for a case fatality ratio of 10%. Sixty per cent of the 30 cases occurred during the summer and early fall months. Geographic clustering was also evident. Hemolytic-uremic syndrome is a rare but endemic disease in Oregon and may occur in small clusters. Although descriptions of several large series of patients have been published, this study describes the first statewide population-based study of this syndrome.