Sarcoidosis is often identified as swollen hilar lymph nodes found in chest radiography during routine physical checkups. We report a patient with concomitant sarcoidosis and lung cancer necessitating thoracoscopic lymph node biopsy to differentiate between sarcoidosis and lung cancer as the cause of mediastinal/hilar lymph node swelling prior to conducting pulmonary lobectomy. Thoracoscopic biopsy of left mediastinal lymph nodes and sampling of frozen sections of right lymph nodes during intraoperative diagnosis did not detect metastasis. A permanent pathological slide, however, indicated that right interlobar (#11s) lymph nodes involved both sarcoidosis and lung cancer metastasis. Despite careful preparation, it thus remains difficult to distinguish between these conditions even when lymph nodes are strictly evaluated.