Abstract Body (Do not enter title and authors here): Bleeding complications represent a significant concern in intensive care settings, with 5-6% of critically ill adults developing major bleeding and up to 85% experiencing minor bleeding events. In critically ill children, previous studies have reported clinically relevant bleeding rates of 9.1%, with surgical patients facing a particularly elevated risk. The management of bleeding risk is particularly challenging in critically ill surgical adolescents, who face a two-fold higher risk of bleeding compared to non-surgical patients. While there is increasing focus on preventing venous thromboembolism through anticoagulation in these patients, the natural history and patterns of bleeding events remain poorly characterized. To address this knowledge gap, we conducted a retrospective observational study of 200 critically ill adolescents aged 13-17 years admitted to four pediatric ICUs following trauma or surgery. Using a validated bleeding assessment tool, we categorized events as major, clinically relevant non-major, or minor. Our study revealed a substantial 53.5% incidence of clinically relevant bleeding, with many events occurring beyond the first 24 hours of admission. The median time to first clinically relevant bleeding was 2 days, notably longer than previous reports. Significantly, NSAID use emerged as a key risk factor (OR 2.68, 95% CI 1.12-6.41), while traditional risk factors showed no significant correlation. These findings challenge existing assumptions about bleeding patterns in critically ill adolescents and provide crucial insights for developing evidence-based guidelines for bleeding prevention and management. The extended timeline of bleeding risk suggests the need for prolonged monitoring and careful medication management in this vulnerable population.