We investigated the validity of thoracoscopic surgery-in patients with primary lung cancer undergoing lobectomy. 14 primary lung cancer patients treated by typical VATS lobectomy and one by anatomical segmentectomy, were compared with 56 patients with Stage-I lung cancer undergoing standard lobectomy (control group), the results focusing on the lymph-nodes dissected. All 14 lobectomy patients showed primary lesions of size less than 3 cm. Following classification of the lymph-nodes into groups I (hilar lymph node) and II (mediastinal lymph node), we compared results according to the sites of the lobectomies conducted. Numbers of dissected lymph-nodes were similar in patients whether undergoing standard thoracotomy or VATS lobectomy. We also investigated what histological types of cancer should be treated by VATS lobectomy by comparing preoperative and operative staging in the control group. The results showed that in most patients with squamous-cell carcinoma judged as T1 N0 M0 the staging corresponded, the other patients actually being in N1 (Stage II). Of Patients with adenocarcinoma of T1 N0 M0, however, 14% had lymph-node metastasis even into the superior mediastinum, i.e., Stage III. The overall findings suggest at present that VATS lobectomy should be applied preferably to patients with a histological typing such as squamous cell carcinoma or alveolar cell carcinoma of relatively early stage, i.e. preoperative Stage I.