BACKGROUND: Retained hemothorax (rHTX) requiring intervention occurs in up to 20% of patients who undergo chest tube (TT) placement for a hemothorax (HTX). Thoracic irrigation at the time of TT placement decreases the need for secondary intervention in this patient group but those findings are limited because of the single-center design. A multicenter study was conducted to evaluate the effectiveness of thoracic irrigation. METHODS: A multicenter, prospective, observational study was conducted between June 2018 and July 2023. Eleven sites contributed patients. Patients were included if they had a TT placed for a HTX and were excluded if: younger than 18 years, TT for pneumothorax, thoracotomy or video-assisted thoracoscopic surgery performed within 6 hours of TT, TT >24 hours after injury, TT removed <24 hours, or death within 48 hours. Thoracic irrigation was performed at the discretion of the attending. Each hemithorax was considered separately if bilateral HTX. The primary outcome was secondary intervention for HTX-related complications (rHTX, effusion, or empyema). Secondary intervention was defined as: TT placement, instillation of thrombolytics, video-assisted thoracoscopic surgery, or thoracotomy. Irrigated and nonirrigated hemithoraces were compared using a propensity weighted analysis with age, sex, mechanism of injury, Abbreviated Injury Scale chest, and TT size as predictors. RESULTS: Four hundred ninety-three patients with 462 treated hemothoraces were included, 123 (25%) had thoracic irrigation at TT placement. There were no significant demographic differences between the cohorts. Fifty-seven secondary interventions were performed, 10 (8%) and 47 (13%) in the irrigated and non-irrigated groups, respectively ( p = 0.015). Propensity weighted analysis demonstrated a reduction in secondary interventions in the irrigated cohort (odds ratio, 0.56 (0.34-0.85); p = 0.005). CONCLUSION: This Western Trauma Association multicenter study demonstrates a benefit of thoracic irrigation at the time of TT placement for a HTX. Thoracic irrigation reduces the odds of a secondary intervention for rHTX-related complications by 44%. LEVEL OF EVIDENCE: Therapeutic/Care Management; Level II.