Recently, routine clinical use of CT scan has enabled the detection of many small pulmonary nodules. Concurrently, high-resolution CT(HRCT) has made great advances in the diagnosis of small peripheral lung cancer. In the tumor of adenocarcinoma, non-invasive bronchioloalveolar carcinoma(BAC) component having a replacement growth pattern of alveolar lining cells shows ground-glass opacity(GGO) on HRCT. On the basis of analysis of small peripheral adenocarcinoma (= < 2 cm), patients with tumors showing > = 50% GGO had no metastatic tendency. Therefore, simple wedge resection may be acceptable as a radical operation. On the other hand, since patients with tumors < 50% GGO had slight metastatic tendency depending upon the tumor size, segmentectomy with mediastinal lymph node sampling should be considered only for tumors = < 15 mm.