Controversy persists regarding the use of antibiotics in association with t tube thoracostomy for trauma patients. We conducted a prospective randomized study of patients requiring tube thoracostomy for pneumo- and/or hemothorax complicating blunt or penetrating thoracic trauma in an attempt to assess the efficacy of prophylactic antibiotic therapy. Fifty-eight patients were included in the study. The control group (Group I) included 28 patients who received no antibiotic therapy: the experimental group (Group II) included 30 patients who received cefoxitin (1.0 gm IV q 6 h) commencing before tube thoracostomy and terminating 12 hours after its removal. The incidence of infectious complications (pneumonia and/or empyema) was recorded. Among the patients not receiving antibiotics, eight of 28 (29%) developed infectious chest complications. Of the patients receiving antibiotics, there was one infectious complication (3%). This difference is statistically significant (p = 0.0227). Cultures demonstrated significant conversion from negative to positive both within each group and between groups. The organism most commonly recovered was S. aureus. Our findings strongly suggest that patients requiring tube thoracostomy for trauma, whether blunt or penetrating, should receive the benefit of systemic prophylactic antibiotic therapy.