Objective: Tonsillectomy is one of the most common surgeries worldwide, mostly indicated for recurrent throat infections and sleep-disordered breathing. The most significant complication is post-tonsillectomy bleeding. Although several risk factors for post-tonsillectomy bleeding in adults have been described, the role of post-operative pain as a risk factor for hemorrhage has not been described in this patient population. Design: Retrospective cohort study of adult patients (18 years and older) who underwent tonsillectomy in a tertiary referral center. Multi-variable logistic regression model was used to test correlation between the independent variables and post-tonsillectomy bleeding. Results: 305 patients (male to female ratio 1:1) with a mean age of 30.5 years old (18-82, ± 12). Mean body mass index was 26.6 (16-42, ±5) and 13% of patients were current smokers. Post-tonsillectomy pain on post-operative day 1 and 2 was associated with increased risk of bleeding (adjusted odds ratio 2.18, 95% confidence interval 1.73-2.44). Other factors that were associated with increased risk of post-tonsillectomy bleeding were male sex, young age (18-30 years old), smoking, recurrent throat infections as an indication for surgery and the usage of hot technique (p < 0.05). Conclusions: Increased post-operative pain following tonsillectomy is associated with increased risk of bleeding in adults. Other factors such as younger age group, males, smoking, previous throat infections and using hot dissection technique are also associated with risk of post-tonsillectomy bleeding. Further studies should explore the effect of strict pain control regimens on post-tonsillectomy bleeding in adults.