Ectopic secretion of adrenocorticotropic hormone (ACTH) related Cushing's syndrome (CS) is more frequently observed than many other paraneoplastic syndromes in patients with small cell lung cancer. Suppression of the cellular immune system in these patients is severe problem for both patients and physicians. In addition, the chemotherapy has been caused to severity and higher rate of hematological toxicity. We present a case of small cell lung cancer having a very poor prognosis, with a compressed humoral and cellular immune system due to an ectopic secretion of ACTH related CS. We report a rare case of combined immunosuppression in a case with small cell lung cancer in this paper. In addition, in the light of this special case and literature, we suggest treatment strategies for small cell lung cancer patients with CS.