We report the case of an 84-year-old woman who was initially admitted to the emergency room of our institution for frank dehydration caused by acute and severe secretory diarrheas along with acidosis and hypokalemia. After extensive gastrointestinal investigations, the etiology of the diarrhea remained unclear. Because clinical symptoms and ionogram parameters worsened, despite intravenous fluids and electrolyte replacement, an abdominal CT scan was performed and unexpectedly revealed a 4.5-cm mass in the right adrenal gland. Several separate 24-hour urine catecholamines were shown to be highly elevated. The diagnosis of pheochromocytoma was confirmed by MIBG scintigraphy and MRI. Before the admission, the patient never experienced symptoms suggestive of pheochromocytoma, except dry mouth and fear of impending death on several occasions. After 2 weeks, the diarrhea stopped abruptly and spontaneously without specific medication but after adequate rehydration. The patient subsequently underwent surgical removal of the adrenal medullary mass. Postoperatively, urinary catecholamines returned to normal values. Immunohistochemical study of the tumor confirmed the diagnosis of pheochromocytoma and revealed the presence of VIP-positive cells organized as islets in scattered areas of the tissue. This case illustrates the protean mode of presentation of pheochromocytoma, as well as the ability of medullary neural crest-derived cells to produce various neuropeptides potentially responsible for a large variety of symptoms.