Episodes of post-tonsillectomy hemorrhage are unpredictable and potentially life-threatening. Primary post-tonsillectomy hemorrhage (< 24 hr postoperatively) is generally considered to be more common and more serious than secondary hemorrhage (> 24 hr). Therefore, recent studies have focused on the control of primary hemorrhage in order to determine the appropriate length of postoperative observation. The issue of follow-up is becoming more important in light of the increasing popularity of outpatient tonsillectomy. We undertook a prospective study to evaluate the incidence of post-tonsillectomy hemorrhage over the short and long term (3 mo). We studied 602 patients, aged 23 months to 89 years (mean: 20.6 yr), who had undergone inpatient tonsillectomy in 1999 and who had been hospitalized for at least 5 days. Our goal was to ascertain the number of episodes of postoperative hemorrhage that required surgical treatment under general anesthesia. We were able to contact 601 of these patients (or their parents) by telephone 3 months postoperatively to inquire about any instances of delayed secondary bleeding. In all, 16 patients (2.7%) had experienced post-tonsillectomy bleeding that required surgically achieved hemostasis under general anesthesia. Of this group, 11 patients (68.8%) had experienced primary hemorrhage and were treated immediately, and five (31.3%) experienced secondary hemorrhage. One patient in the latter group experienced excessive bleeding 38 days postoperatively, which we believe is the latest episode of secondary bleeding reported to date. Based on the findings of this study, we believe that a postoperative follow-up period of 10 days is sufficient to identify all but the most rare cases of post-tonsillectomy hemorrhage.