Out of 858 patients who underwent thoracotomy for primary lung cancer, 279 cases were classified as non-curative on the basis of intraoperative and/or post-operative examinations. The causes for non-curative resection were defined as follows: (I) absolutely non-curative resection, (1) palliative tumor extirpation (palliative), (2) remaining tumor in (a) lymph nodes (Ly rem), (b) chest wall or diaphragm (Ch/Dia rem), or (c) bronchial stump (Bro rem), (3) intrapulmonary metastasis (PM), (4) pleural dissemination or pleuritis carcinomatosa (P1/Diss), (5) metastasis in other organs (Meta); (II) relatively non-curative resection, (1) incomplete resection of lymph nodes (R0-1), (2) group 2b or 3 lymph node metastasis (2b Ly). The 5-year actuarial survival rate of the Bro rem group was 35.6%, being the best among the absolutely non-curative cases, followed by the PM group (33.7%), the Pl/Diss group (31.6%) and the Ch/Dia rem group (29.7%). The results of the Ly rem and Meta groups were poor at 5.4% and 0%, respectively. Those of the relatively non-curative group were 24.4% (R0-1 group) and 11.6% (2b Ly group). Non-curative resection is not the treatment of choice, but by analyzing the causes of non-curative resection, we may able to improve the prognosis of advanced cases of lung cancer.