Background: A pleural effusion is not a disease entity but a clincial sign of systemic or pleural disease. Although the diagnosis of pleural effusion can often be done by toracentesis and pleural needle biopsy the yeild of positive diagnosis is low. <aterial and Method: The authors retrospectively reviewed 58 consecutive patients(59 cases) for diagnostic thoracoscopy from August 1992 to march 1997. Retrospective data were collected in respect to present symptoms thoracoscopic gross findings final pathological findings amount o drainage and complications of the procedure. Result: Final diagnosis were as follows: 24 nonspecific chronic inflammations 17 tuberculouses 10 metastatic carcinomas 5 granulomatous inflammations 1 malignant mesothelioma and 2 negative pathologies, The diagnostic sensitivity for malignant disease was 91% and the specificity 100% For pleural tuberculosis both the sensitivity and specificity were 100% No association could be identified between the gross observations at the time of thoracoscopy and the final diagnosis. There were no in-hospital deaths or major complications related to the procedure. conclusion: Diagnostic thoracoscopy is a useful modality for diagnosis of effusions of unknown origin where other methods have failed. Thoracoscopy involves inspection of the visceral and parietal pleural surfaces under direct vision. Thoracoscopy is a safe effective and relatively simple procedure which can be easily performed under direct vision. Thoracoscopy is a safe efficitive. and relatively simple procedure which can be easily performed under regional anesthesia even in ill or elderly patients.