A typical three generation-family with MEN 2A (Multiple Endocrine Neoplasia, Type 2A) is described. Two brothers and their uncle were affected with medullary thyroid carcinoma (MTC) and pheochromocytoma. The diagnosis of MTC was based on calcitonin determinations after pentagastrin stimulation. Pheochromocytoma was clinically silent in two cases. A family screening with pentagastrin test led to the diagnosis of C cell hyperplasia in a 8-year boy, who was then successfully operated on. The authors discuss the value of pentagastrin test and genetic testing in the early diagnosis of MTC associated with MEN 2A syndrome.