The role of medical thoracoscopy in the diagnosis by pleural diseases is increasingly being recognized. This study was done to assess the role of medical thoracoscopy in the diagnosis of undiagnosed pleural effusion patients by pleural biopsy from abnormal pleura under direct vision. Materials and Methods: We analyzed retrospectively data of 65thoracoscopic pleural biopsy performed at our centreon patients with undiagnosed pleurisy in the past 18 months. Medical thoracoscopy was performed under conscious sedation with midazolam (2 mg) and fentanyl (50 mcg) and local anesthesia with lignocaine 2% (10–15 ml), through a single port 10 mm diameter thoracoscope. Results: A total of 65 patients (48 males and 17 females) underwent medical thoracoscopy during the study period. The mean age was 47.5(range, 18–72). The final diagnosis by thoracoscopic pleural biopsy was made in 59 (90.7%) patients and infective pathology were confirmed in 42 (tuberculosis in 24, parapeumoniceffusion in 8 and nonspecific inflammation in 10), malignancy in 17 patients and 6 remained undiagnosed. There were no major procedure-related complications that required intervention. Conclusion: Pleural effusion without diagnosis after initial evaluation is a frequent problem in a respiratory division, for which thoracoscopic pleural biopsy is regularly necessary. Medical thoracoscopy has a high diagnostic yield, and is generally safe, certainly compared with the diagnostic and therapeutic importance.