Of a series of resected primary lung cancer at the hospital in a recent 9-year period from January 1986 to December 1994, 90 patients with non-small cell lung cancer underwent “absolutely curative resection” and 72 non-small cell lung cancers underwent “relatively curative resection”. In order to elucidate the prognostic factors, these cancers were evaluated for age, sex, tumor size, pathologic T factor, pathologic N factor, histopathological features, and method of detection. Fifteen of the 90 (17%) patients developed recurrence which was examined for the presence of vessel invasion and involvement of visceral pleura. All of these 15 recurrent cases had evidence of lymphatic vessel invasion. Six of these 15 cases (40%) also had blood vessel ilmvasion. The mean size of the tumors was significantly larger in the recurrent cases after absolutely curative resection than that in all resected cases. However, there was no significant difference between the recurrent cases and all cases of curative resection in the presence or absence of involvement of visceral pleura. Multivariate analysis of all risk factors revealed that the T factor and the presence of vessel invasion are only independent risk factors for recurrence after curative resection. In conclusion, it is important for preventing recurrence after curative resection to detect the tumor in smaller size, to avoid the growth or invasion of the tumor due to delayed treatment, and to perform complete resection with mediastinal lymph node dissection as early as possible.