A 69-year-old woman was diagnosed with sarcoidosis, which was not treated with corticosteroid therapy. Her levels of angiotensin converting enzyme decreased significantly over 4 years and a mass lesion was detected near the lower part of her left main bronchus, and diagnosed as small cell lung cancer (SCLC). Treatment of the SCLC with a series of chemotherapeutic agents produced excellent results. The pulmonary sarcoidosis did not show any deterioration despite the frequent use of amrubicin, which is known to be a cause of interstitial pneumonia. This is a case report of SCLC complicated with sarcoidosis in a stage of spontaneous remission, possibly suggesting an association between sarcoidosis and tumor immunity, since recent reports have suggested that immune checkpoint inhibitors might be involved in the development of sarcoidosis. (J Nippon Med Sch 2018; 85: 291 296)