Objective       To evaluate the diagnostic value and safety of medical thoracoscopy for pleural effusion with unknown origin.       Methods        Clinical data of 548 cases of pleural effusion with unknown origin and without identified diagnosis who undergoing medical thoracoscopy for diagnosis in our department from December 2009 to June 2013 were collected in this study. The rate of final diagnosis and complication and the sequelae of whose diagnosis undetermined were retrospectively analyzed

and the results were contrasted to 277 cases of closed pleural biopsy performed from January 2007 to November 2009 in order to evaluate the diagnostic value and security of medical thoracoscopy for pleural effusion with unknown origin.       Results       The diagnostic rate was significantly higher in the medical thoracoscopy group than in the closed pleural biopsy group [88.9% (487/548) vs 61.7% (171/277)

Chi square=83.918

P=0.000]. The failure rate was obviously lower in the former than the latter [1.1% (6/548) vs 6.8% (19/277)

Chi square=16.312

P=0.000]. However

there was no difference in the incidence of complication between the 2 groups [16.8% (92/548) vs 14.1% (39/277)

Chi square=1.011

P=0.315]. The cure rate of diagnostic anti-tuberculous treatment for undiagnosed cases was remarkably higher in the medical thoracoscopy group than in the closed pleural biopsy group [78.8% (26/33) vs 57.0% (49/88)

Chi square=4.109

P=0.043].       Conclusion       Medical thoracoscopy is a safe examination approach with high diagnostic yield and low rate of complications for pleural effusion with unknown origin

and it can guide further therapy strategy for undetermined cases.