We conducted a retrospective study of 4,848 patients to evaluate the age-specific incidence of post-tonsillectomy hemorrhage that required surgical treatment. We reviewed the charts of 2,567 patients younger than 15 years (pediatric group) and 2,281 patients aged 15 years and older (adult group) who had undergone tonsillectomy with or without adenoidectomy. We found that post-tonsillectomy hemorrhage occurred significantly more often in the adult group (3.9 vs 1.6%; p < 0.001). Moreover, primary hemorrhage (< 24 hr postoperatively) was also significantly more common in the adult group than in the pediatric group (82.9 vs 65.9%, p = 0.023). Analysis of other parameters revealed that post-tonsillectomy hemorrhage was significantly more common in males and in patients who had a history of chronic or recurrent throat infection. Awareness of these risk factors should help improve patient care and outcomes.