ABSTRACT Background Treatment of stable patients with penetrating chest trauma caused by stab wounds is based on clinical observation and radiological follow-up. Classically, X-rays have been used at patient admittance and 6 hours after to detect hemothorax and pneumothorax not detected initially. Nevertheless, previous studies have explored the possibility of reducing follow-up time to 3 hours. This study compares 3 hours and 6 hours radiological follow-up to test the hypothesis that 3 hours follow-up is as safe interval than 6 hours for definitive management of stable patients with stab wounds in the chest. Materials and methods This is a prospective study conducted for 7 months from August 2010 through March 2011. Of the 162 eligible patients, 146 completed the protocol. Upon hospital admission all patients were clinically examined and evaluated with chest X-rays. Three hours and 6 hours follow-up X-rays after the trauma, in the Emergency Department, were taken of all patients radiologically assessed at admittance. We excluded patients with associated injuries requiring surgical intervention and we compared the findings of the two follow-up intervals. Results There were 225 stab wounds in the 146 patients evaluated. Average age was 29 years. One hundred and thirty-one patients had normal X-rays at admittance that did not change after 3 hours or 6 hours follow-ups. Fifteen patients presented hemothorax or pneumothorax in follow-up X-rays, 14 of them presented evident change in 3 hours X-ray follow-up. The only patient, whose lesion was evident in the 6 hours follow-up X-ray, but not the 3 hours follow-up X-ray, had a small asymptomatic pneumothorax, which did not require thoracic drainage. Conclusion No patients of 146 evaluated in our study developed traumatic pleuropulmonary injuries after 3 hours of follow-up that required pleural drainage or other intervention. Our results suggest that shortening the follow-up time from 6 to 3 hours for stable patients with chest stab wounds is safe, cost-effective and can help decongest emergency services. Level of evidence Therapeutic/care management study, level II. How to cite this article Facundo GH, Martinez SI, Carvajal C. Treatment of Stable Patients with Penetrating Chest Trauma Caused by Stab Wounds: Three vs six Hours Follow-up. J Trauma Critical Care Emerg Surg 2013;2(3):101-105.