To assess a hepatitis B vaccination program offered to all grade 6 students in British Columbia in 1992. Cohort study. British Columbia, Canada. All grade 6 students were offered vaccine. Subsets of 454 and 259 students participated in studies of minor adverse events and seroresponse, respectively. The vaccine used was Engerix-B, 20 micrograms, given at intervals of 0, 1, and 6 months. Province-wide acceptance and series completion rates and reports of severe adverse events. Minor adverse events and immunogenicity in subsamples. A total of 127,922 vaccine doses were administered. Initial enrollment totaled 43,358 students or 95.4% of those eligible. The series was completed by 41,594 students (95.6%). Minor adverse events were infrequent in the cohort assessed: no absenteeism or physician visits resulted from vaccination. Sixty-nine reported severe adverse events met surveillance definitions, the major categories being injection site reactions (23% of reports), fainting (20%), and rashes (17%). There was one instance of anaphylaxis. Only 13 of these events resulted in recommendations to discontinue the series. Of students tested following the series, 98% had levels of antibody to hepatitis B surface antigen considered to be protective (> or = 10 IU/L), the geometric mean titer being 690 IU/L (95% confidence interval, 498 to 957 IU/L). Our experience indicates that school-based programs for universal vaccination of preadolescents can be highly acceptable and efficient.