Sixty-four (14.7 percent) of 434 consecutive patients having pulmonary resection for bronchogenic carcinoma were found to have microscopic residual tumor on the cut margins of the resected specimens. These subjects were further subdivided histologically into those with direct extension of the tumor (34 patients), lymphatic permeation (14 patients), clumps of cancer cells in parabronchial tissues (six patients), and the presence of carcinoma in situ change (10 patients). Bronchopleural fistulas developed in eight (12.5 percent) of 64 patients. The operative mortality rate was 15.6 percent, with four of the deaths occurring as the result of bronchopleural fistulas. Thirty-two patients (50 percent) survived 1 year, 21 (32.8 percent) survived 3 years, and 15 (23.4 percent) lived for 5 years or more. The patients with tumor in the submucosal and peribronchial lymphatics had the worst prognosis. 78.6 percent having died within 1 year and the remainder within 3 years. All 5-year survivors were men with squamous cell carcinoma and had relatively small tumors (mean diameter 2.9 cm). No direct relationship between the length of the resected bronchial stump and survival could be established; a short stump did not preclude long survival. The possible factors involved in the relatively high 5 year survival rate in this group of patients and the therapeutic implications of these factors are discussed.