Of 104 patients evaluated for thoracic sepsis by CT, 22 patients had both CT and clinical evidence of mediastinal infections. The CT findings in these patients were reviewed and compared with a control group of seven postoperative patients following uncomplicated median sternotomy. Based on CT appearance, patients were classified into one of three groups: (a) diffuse soft tissue infiltration with or without gas (i.e., mediastinitis) (10 patients); (b) focal mediastinal abscess (four patients); (c) mediastinal infection associated with empyema or subphrenic abscess (eight patients). Computed tomography proved reliable in distinguishing diffuse mediastinitis from a localized drainable abscess. However, in the absence of mediastinal gas, CT could not differentiate mediastinitis from benign postoperative changes. Computed tomography was helpful in identifying associated empyemas and a variety of other secondary complications. In five of six patients with mediastinal abscess, CT demonstrated communication or contiguity with four empyemas and one subphrenic abscess. Closed chest tube drainage of the empyemas and percutaneous drainage of the subphrenic abscess combined with antibiotic therapy were successful in treating the mediastinal abscess in these five patients. Although overall mortality for mediastinal infection in this series was 27%, there was a 50% mortality for patients with diffuse mediastinitis.