Of the 183 patients with primary lung cancer treated at our hospital with small peripheral lung cancers of 3 cm or less in diameter: 16 had tumors up to 1 cm, 23 had tumors of 1-1.5 cm, 43 had tumors of 1.5-2 cm, and 101 had tumors of 2-3 cm in diameter. These tumors comprised 134 adenocarcinomas, 31 squamous cell carcinomas, 6 adenosquamous carcinomas, 4 small cell carcinomas, 2 large cell carcinomas and 6 carcinoids. The tumor classification was 134 n0, 20 n1, and 29 n2 tumors. As tumor size is smaller, n0 tumors, p0 + p1 tumors and ly0 tumors are significantly increased. All tumors of up to 1 cm in diameter exhibited no node or intrapulmonary metastases and never resulted in the death of the patients due to lung cancer: thus good prognoses may be expected in such cases. In tumors larger than 1 cm in diameter, node or intrapulmonary metastases are increased and 5-year survival rates are decreased. In multivariate analysis the most effective factor on prognosis is node metastasis. For better post-operative prognosis, we may have to detect and resect peripheral lung cancers in the stage of tumor size of up to 1.5 cm in diameter, because node metastases are rare in these small tumors.