The prognosis of lung cancer patients who are not candidates for surgery is usually poor. The unfavorable natural history of respiratory failure in this group of patients has been suggested as a causative factor. We analyzed the outcome of 46 consecutive patients with primary lung cancer on whom mechanical ventilators were utilized. Although seven patients were ultimately weaned and survived for at least 24 hours, three of them subsequently died prior to discharge from the hospital. The remaining 39 patients died while using the ventilator. Patient age, tumor cell type, and the etiology of respiratory failure were not significantly different between the weaned and unweaned populations. A difference was noted in the duration of mechanical ventilation: none of the patients who could be weaned required mechanical ventilation for more than six days (range, two to six days). Respiratory failure in the nonsurgical lung cancer patient carries a poor prognosis, and selection of patients for mechanical ventilation should be conservative.