In the present study, influences of pleural adhesions on thoracoscopic lung surgeries were investigated. A total of 666 consecutive patients who had undergone thoracoscopic surgeries for lung malignant tumors were retrospectively analyzed. Pleural adhesions were present intraoperatively in 289 cases, of which 6 required conversion to thoracotomy due to the adhesions. The influences of pleural adhesions on the perioperative period were comparatively large under following conditions (level-A); the adhesion-type was tight which meant lung and pleural wall sticked closely even if lung collapse was encouraged, the strength was middle( required sharp-dissection) or strong( hard to dissect between visceral and parietal pleura), and the range was more than 10% of total pleural surface. Significant influences of the level-A of pleural adhesions were as follows;prolonged operation time in all procedures, frequent intraoperative lung fistula and prolonged pleural drainage period in wedge resections, and increased blood loss, intraoperative and postoperative lung fistula with prolonged pleural drainage time and postoperative hospitalization period in lobectomy. Other postoperative complications (pneumonia, empyema, exacerbation of interstitial pneumonitis, and arrhythmias) were not associated with pleural adhesions. Careful dissection procedure for pleural adhesions that minimize damage of visceral pleura would be the most important.