Background : To evaluate exudative pleural fluid, thoracentesis for microbiological and cytological examination and pleural biopsy by using a Cope needle are traditionally performed. Even after these studies, about 20% of patients remain undiagnosed. We evaluated the diagnostic accuracy and complications of 2-mm minithoracoscopy instead of blind biopsy in patients with undiagnosed exudative pleural effusion. Method : Fifteen patients with exudative pleural effusion underwent thoracoscopy between April 2002 and August 2003. The indication was undiagnosed pleural effusions after having performed sputum and pleural fluid exami-nations both microbiologically and cytologically. Results : The median age of the patients was 56 years (range 21-77). Pleural effusions were lymphocyte-dominant in 11 patients (73.3%) and neutrophil-dominant in 3 (20.0%). The remaining patient (6.7%) had pleural-fluid eosinophilia. Minithoracoscopic biopsy revealed accurate diagnosis in 14 patients (93.3%), consisting of tuberculous pleurisy in 8 (66.7%), malignant effusions in 4 (33.3%), and parapneumonic effusions in 2 (13.3%). One was diagnosed as having paragonimiasis from thoracoscopic findings and clinical considerations. There was no procedure-associated mortality. There were six cases of new onset fever (40%) and one of pneumothorax (6.7 %). Conclusion : Two-millimeter minithoracoscopy, which is less invasive than conventional thoracoscopy, was an accurate and safe method for undiagnosed exudative pleural effusion.