A 40-year-old woman was presented with a fever, which proved to be due to mediastinal tuberculous lymphadenitis. Up to 1988, 149 cases of tuberculous mediastinal lymphadenitis have been reported in the literature in Japan. This case was very rare because a chest plain film revealed neither mediastinal widening nor lung parenchymal involvement. On the other hand, a CT scan of the chest was very useful because it showed unsuspected mediastinal lymph nodes enlargement. The diagnosis of tuberculous mediastinal lymphadenitis was made by the findings of a supraclavocular lymph node biopsy, which showed granulomas, compatible with tuberculosis. A good response from the patient to antituberculous therapy confirmed this diagnosis.