Undifferentiated carcinoma of the lung carries a worse prognosis overall than other cell types, but it is unclear whether these tumors represent a homogenous group with uniformly poor survival. This study identifies certain histologic subtypes of large cell and small cell undifferentiated carcinoma which have a better prognosis after curative resection than other similarly treated undifferentiated carcinomas. From 1947 through 1975, a total of 2,352 patients with lung cancer were admitted to one hospital. Follow-up to death was available in 98%. Pathological material was reviewed from 1,979 cases by a team of three pathologists during a single 6-month period without knowledge of clinical outcome. Curative resection was carried out in 632, with 170 (27%) 5-year survivors. Small cell cancer occurred in 481 patients and 9 (1.6%) survived 5 years. Curative resections were performed in 34 with polygonal small cell carcinoma, 20 with normal lymph nodes and 14 with diseased lymph nodes. Seven survived 5 years (21%), 6 of 20 with normal and 1 of 14 with diseased lymph nodes. Eleven with nonpolygonal small cell carcinoma (8 oat cell, 3 fusiform) (5 normal, 6 diseased nodes) underwent curative resection, with no survivors. Large cell carcinoma occurred in 151 and 19 survived 5 years. Curative resection was performed in 24 having large cell carcinoma with stratification (16 normal, 8 diseased nodes), and 12 (50%) survived 5 years. In 26 with nonstratified large cell carcinoma undergoing curative resection (18 normal, 8 diseased nodes), 6 (23%) survived 5 years (χ2 = 4.06 p < 0.05). Thus patients with resectable polygonal small cell carcinoma appear to have a better prognosis than those with nonpolygonal small cell carcinoma, and their prognosis approaches that of all patients with resectable lung cancer. Patients having resectable large cell carcinoma with stratification have a significantly better prognosis than those with nonstratified large cell carcinoma. Patients with these subtypes should therefore not be denied an attempt at curative resection because of the diagnosis of undifferentiated lung cancer.