PURPOSE: Adult trauma literature indicates hemothorax volume >300 mL requires thoracic drainage. Due to a paucity of pediatric literature, we aim to analyze pediatric traumatic hemothorax management and calculate a volume threshold requiring chest tube placement. METHODS: Pediatric traumatic hemothorax cases from two level 1 trauma centers were analyzed. Management was categorized into successful observation (SO), chest tube placement (CTP), and failure of initial observation (FO). Hemothorax volume was calculated using Mergo's formula: d2xl. d = greatest depth on transverse cuts. l = length on sagittal cuts. Hospital course, postoperative and long-term outcomes were measured up to 1 year. RESULTS: 406 traumatic thoracic cases were identified, with 74 hemothoraces analyzed: 32 (43 %) SO, 38 (51 %) CTP, 4 (6 %) initial operation, 10 (12 %) FO. We observed increases in injury severity score (p = 0.020) and thoracic abbreviate injury scale (p < 0.001) in CTP versus SO. Presenting tachypnea was not associated with chest tube placement (p = 0.632). Statistically higher hemothorax volume was found in CTP vs SO (142.7 mL vs 19.5 mL, p < 0.001). Utilizing ROC Curve analysis, >55 mL measured with Mergo's formula predicted chest tube placement (p = 0.001). Chest tube placement was associated with increased mechanical ventilation requirement (p < 0.001), hospital length of stay (LOS) (p < 0.001), and ICU LOS (p < 0.001). No patients developed delayed empyema from retained hemothorax. CONCLUSIONS: This is the largest cohort of pediatric traumatic hemothoraces and first in the literature to calculate volume threshold requiring chest tube placement. Judicious application of hemothorax volume calculation and overall injury score may assist in the decision making of pediatric traumatic hemothorax management. TYPE OF STUDY: Retrospective Observational Cohort Study. LEVEL OF EVIDENCE: Level 3 evidence.