In a retrospective study of 687 computed tomographic (CT) examinations of the chest and abdomen performed over a 1 year period, 16% of the examinations produced information not otherwise available which altered patient diagnosis, prognosis, or therapy. Sixteen thoracotomies and 18 laparotomies were avoided as a result of information available only from CT examinations. CT was of particular value in the evaluation of mediastinal masses, in the assessment of suspected or proven lung cancer, and in the evaluation of pleural and extrapleural masses. It was of notable clinical value in evaluating patients with intraabdominal abscesses, pancreatic disease, staging of malignancies for radiation therapy and surgery, and excluding the presence of suspected masses.