Ectopic ACTH production occurs in about 10% of all cases of Cushing's syndrome, and about 25% of cases of ACTH-dependent Cushing's syndrome. Diverse tumor types are able to produce ACTH ectopically, including small cell lung carcinoma. Ectopic ACTH secretion by malignant neoplasm has been reported to have earlier and more aggressive metabolic effects. We report a 59-year-old male patient with severe hypertension, metabolic alkalosis and hypokalemia as the first clinical manifestations of an ACTH-secreting small cell lung carcinoma, although the typical phenotypic features of Cushing's syndrome were not present. Ectopic Cushing's syndrome should always be ruled out in patients with severe hypertension and hypokalemia.