Small cell lung cancer(SCLC) is frequently associated with paraneoplastic syndromes, which occur in approximately 20% of patients at presentation. Clinical Cushing's syndrome secondary to ectopic ACTH production is uncommon, occurring in approximately 5% of all SCLC patients. However, biochemical evidence of hypercortisolism can be detected in up to 50% of patients. Patients with Cushing's syndrome from ectopic ACTH production show hypertension, weakness, hyperglycemia, and hypokalemic metabolic alkalosis, but differ from patients with classic Cushing's disease in that symptoms develop more rapidly. Ectopic ACTH production is associated with a poor response to chemotherapy, short survival, and a high risk of treatment-related complications. We report a case of Cushing's syndrome associated with ectopic corticotropin production in 59-year-old male patient with extensive stage of SCLC.