Mediastinoscopy is the gold standard for diagnosis in the absence of parenchymal lesions in mediastinal tuberculosis lymphadenitis. During mediastinoscopy biopsy, tuberculous bacillus seeding into the mediastinum is a rare complication. This study aimed to test the safety of mediastinoscopy in terms of Mycobacterium tuberculosis seeding in the mediastinum by microbiologically evaluating mediastinal lavage samples taken before and after biopsy. Classical cervical mediastinoscopy was performed all of patients and who were reported as granulomatous inflammatory events results of histopathological examinations and who underwent mediastinal lavage before and after biopsy, were included in the study. All the lavage fluids were tested for AFB and subjected to Mycobacterium tuberculosis PCR DNA testing and standard tuberculosis culture. The patients were divided into two groups, Group 1: Necrotizing granulomatous inflammation, Group 2: non-necrotizing granulomatous inflammation. The microbiological tests of the patients in Group 1 were negative before biopsy. However, in two patients of Group 1, the results of cultures of lavage fluids that taken from after biopsy were positive for tuberculosis. In all patients in Group 2, all microbiological tests of the lavage fluids were negative (Power of the decision: 99.8%, with 5% error). All of patients in group 1, Antituberculosis treatment was initiated and continued for 6 months. There weren’t seen any serius complications due to treatment and recurrence during the follow-up period. Mediastinoscopy can be used safely, with low morbidity and mortality rates and a high success rate for the diagnosis of mediastinal tuberculosis.