Mediastinal lymphadenopathy in a patient with previously treated T-cell acute lymphoblastic leukaemia is a diagnostic problem. The differential diagnosis in an adult is sarcoidosis, metastases, lymphoma or, rarely, tuberculosis. Mediastinal lymph node involvement is uncommon in tuberculosis. In view of its relative rarity but good prognosis, it is important to distinguish tuberculous mediastinal lymphadenitis in adults from other causes of mediastinal masses.