• We retrospectively studied 49 patients who were discharged from Sainte-Justine Hospital, Montreal, Canada, or who died between 1970 and 1987 with a presumptive diagnosis of Reye's syndrome. Reye's syndrome was defined as certain, probable, unlikely, or excluded according to clinical, biological, and histologic criteria agreed on a priori by a panel of experts. Patient charts were reviewed blindly by three clinicians. Assessments were similar in 42 cases (86%) (weighted κ = 0.78 to 0.85, which suggested substantial agreement); for the remainder, agreement was reached after discussion. Reye's syndrome was considered certain in 1 case (2%), probable in 11 (22%), unlikely in 21 (43%), and excluded in 15 (31%). Four children in the study group did not undergo biopsy or autopsy; in three of these, Reye's syndrome was unlikely according to clinical and biological criteria, and in one, the diagnosis was unclassifiable. The incidence of certain or probable Reye's syndrome was low in our institution during the study period. Our results suggest that the apparent disappearance of Reye's syndrome should be reassessed.