Multiple Endocrine Neoplasia type IIa (MEN IIa) is an autosomal dominant syndrome characterized by pheochromocytoma, medullary thyroid carcinoma and hyperparathyroidism. Pheochromocytoma occurs in approximately 50% of patients with MEN IIa. This tumor has the capacity to produce ACTH ectopically and manifests as the Cushing syndrome, although it is very rare. We report a 26-year-old woman patient with severe muscle weakness, skin lesions in extremities, hypertension, and new onset diabetes whose laboratory findings included hypokalemia, metabolic alkalosis, high serum level of cortisol, metanephrine, normetanephrine, calcitonin and bilateral adrenal mass in computed tomography as the first clinical manifestations of an ACTH-secreting pheochromocytoma. In the patients with hypertension, new onset diabetes and hypokalemia, the Cushing syndrome and pheochromocytoma should always be ruled out.