background: the aim of this study was to evaluate the incidence of pleural empiema associated with tube thoracostomy on patients with isolated chest injury, with or without the use of associated antibiotic therapy. method: using cohorts accompaniment statistical model, the authors analysed 167 patients with blunt or penetrating chest trauma. two groups were selected for this study. control group included 104 (62.3%) patients without antibiotic therapy; the experimental group, 63 (37.7%) patients, received cefalotin postopertively (500mg iv; every 6 hours). results: twelve (7.2%) presented blunt trauma; 98 (58,7%) were stabbed, 41(24.6%) were wounded by fire arms; 16 (9.5%) injuries were associated with other type of accidents. the average length of stay for the control group in was 5.7±3.2 days, and for the antibiotic group was 5.7±2.9 days. the results showed that eight patients evolved with the pleural empyema, being seven cases from the control group, and only one from the experimental group (p=0.02). clotted hemotorax was the most frequent non infectious complication occurring on 21 (12.5%) patients. conclusions: the use of antibiotics were not effective on lowering the incidence of pleural empyema on patients that submitted to post-traumatic pleural drainage.