A patient with neurofibromatosis type 1 and watery diarrhoea syndrome due to a VIP-producing adrenal phaeochromocytoma (Case Report). J Intern Med 1999; 246: 231-234. A 43-year-old patient with neurofibromatosis type 1 suffered from watery diarrhoea syndrome induced by excessive production of vasoactive intestinal polypeptide (VIP) in an adrenal phaeochromocytoma. This case report emphasizes that patients with neurofibromatosis are prone to develop more than one disease induced by tumours originating from the neural crest. Since excessive VIP production in a phaeochromocytoma may mask the symptoms of catecholamine overproduction, and in view of the therapeutic consequences, neurofibromatosis patients with hyperVIP-aemia must be checked for the presence of a phaeochromocytoma.