A 28-year-old female patient visited hospital with complaints of fever, loss of appetite, and weight loss that lasted for 1 month after 5 years and 8 months of treatment for the first relapse of subcutaneous panniculitis-like T-cell lymphoma. Computed Tomography (CT) revealed mediastinal necrotic lymphadenopathy, and video-assisted thoracic surgery (VATS) biopsy of the relevant area was performed. Pathologic diagnosis was mediastinal tuberculosis, not relapse. Symptoms of tuberculosis infection can be confused with those of cancer, which can delay diagnosis. We report a case of a patient who had undergone treatment after a first relapse of subcutaneous panniculitis-like T-cell lymphoma and was at risk for relapse but was finally diagnosed with tuberculosis after biopsy.