ObjectiveTo compare the accuracy and safety of semirigid thoracoscopy and rigid thoracoscopy in the diagnosis of unexplained pleural effusion. MethodsA prospective randomized study was conducted, in which the patients with unexplained pleural effusion were enrolled consecutively from March 2012 to March 2014 in West China Hospital. The age of the patients ranged from 18 to 75 years. After informed consent, the subjects were randomized to a semirigid thoracoscopy group or a rigid thoracoscopy group to be examined. ResultsForty-nine patients were assigned to the semirigid thoracoscopy group, and 48 patients were assigned to the rigid thoracoscopy group. After thoracoscopy procedure, 44 patients were confirmed as malignant diseases, and 48 patients were confirmed as benign diseases. The overall diagnostic accuracy was 93.9% for the semirigid procedure and 95.8% for the rigid procedure. The diagnostic sensitivity and specificity for malignancy were 96.0% and 100.0% for the semirigid thoracoscopy, and 95.2% and 100.0% for the rigid thoracoscopy, respectively, without statistical significant differences between two groups. All the patients tolerated well with minor complications after two kinds of thoracoscopy. ConclusionsThe diagnostic accuracy of semirigid thoracoscopy and rigid thoracoscopy is comparable in the diagnosis of unexplained pleural diseases. The samples obtained by semirigid thoracoscopy are smaller, but adequate for pathological examination.