Background: Differential diagnosis between tuberculous pleurisy (TBP) and non- tuberculosis pleural effusion represents a critically important clinical problem. In recent years, several noninvasive methods have been found for diagnosis of tuberculous pleurisy. This study aimed to evaluate the value of detection of the genome of Mycobacterium tuberculosis (MTB) by polymerase chain reaction (PCR) method for the diagnosis of tuberculous pleurisy and compare the results with those of conventional methods. Materials and Methods: In this cross-sectional study, we studied 62 patients (42 men and 20 women) with pleural effusion in Ghaem Hospital, affiliated to Mashhad University of Medical Sciences from January 2006 to June 2007. Results: A total of 20 patients had tuberculous pleurisy (45.4%), 15 patients had malignant pleural effusion (34%), 3 patients had pleural effusion with various “non-tuberculosis non-malignant” etiologies (6.8%) and 6 patients had transudative pleural effusion (13.6). The sensitivity, specificity, positive predictive value and negative predictive value of PCR in tuberculous pleurisy were 85%, 100%, 100% and 88.8%, respectively. Conclusion: The value of PCR test and pleural biopsy was similar in the diagnosis of TBP. However, PCR detected MTB in pleural effusion when conventional pleural biopsy failed to do so. (Tanaffos2011; 10(1): 12-18)