The diagnosis of pleural diseases is one of the frequent clinical problems. Despite a variety of diagnostic tests are available for evaluating pleural effusions, approximately 15– 20% of pleural effusions remains undiagnosed, In this cases ,a thoracoscopy plays an important role, it permits the surgeon to visually view and evaluate the entire pleural space ,and to obtain enough accurate biopsies from suspected areas. This study aims to evaluate the effectivenes of Video Assisted Thoracoscopic surgery (VATS) in diagnosis of pleural effusions. Between June 2012 and June 2015 we performed 38diagnostic thorososcopy for undiagnosed pleural effusions. The histopathologic studies of pleural biopsies result were as follows : )%60,5 ( malignancies,)%31,6 ( TB And )%7,9 ( nonspecific inflammatory reaction. The malignant diseases are: Mesothelioma )%60,9(, Metastases of adenocarcinoma )%30,4(,Lymphoma )% 8,7( 4 Complications ,with no mortality. Conclusion: Video Assisted Thoracoscopic Surgery is a safe and accurate diagnostic procedure for pleural diseases but it also has a very useful role in therapy.(VATS) saves time, effort and cost, more over it is preferred by the patient as he recovers and returns to his normal activity rapidly.