['Mechanical pleurodesis is widely used to treat primary spontaneous pneumothorax to decrease postoperative recurrence after thoracoscopic bullectomy, but it is unclear whether it actually reduces primary spontaneous pneumothorax recurrence. We aimed to investigate the effectiveness of mechanical pleurodesis after thoracoscopic treatment of primary spontaneous pneumothorax.', 'In our parallel-group, prospective, randomized, controlled trail at 2 hospitals in China, 289 patients were enrolled from January 2010 to January 2013. Patients were randomly assigned (1:1) to receive thoracoscopic wedge resection only (WR group) or thoracoscopic wedge resection and mechanical pleurodesis (WR+MP group). This trial is registered with ClinicalTrial.gov (NCT01463553).', 'Intraoperative bleeding and postoperative pleural drainage were significantly lower in the thoracoscopic WR only group. Postoperative recurrence rate did not significantly differ between groups (log-rank test p=0.791; Breslow test p=0.722). In the thoracoscopic WR only group, no recurrences were found when bullae were isolated or limited; recurrence was 7.5% with the presence of multiple bullae. Younger patients had an increased risk of recurrence (relative risk 3.015; 95% confidence interval 1.092 to 8.324).'] Does mechanical pleurodesis reduce recurrence of spontaneous pneumothorax : a randomized trial?