Combination therapy for nosocomial pneumonia with a β-lactam and aminoglycoside is widely accepted because of synergy and reduction of resistant bacteria. This prospective study of 109 trauma patients (94 blunt, 15 penetrating) with nosocomial pneumonia was performed in consecutive phases. In phase 1, patients were randomized to an anti-pseudomonal third-generation cephalosporin—cefoperazone or ceftazidime. Gentamicin was added to each regimen in phase 2. The mean age of the patients was 37 years, the mean ISS was 31, and there were no differences among the four treatment groups relative to associated injuries. Patients receiving monotherapy had a 56% cure rate compared with 31% for combination therapy (p