The syndrome of multiple endocrine neoplasia (MEN or MEA) type 2b is characterized by the association of medullary carcinoma of the thyroid, phaeochromocytoma, ganglioneuromatosis and Marfan-like features. Though this disorder usually shows a familial distribution, it may also appear spontaneously as the result of a genetic mutation. This paper describes the second case of MEA type 2 in twins, and appears to be the first description in twins of the association of medullary carcinoma of the thyroid, Marfan-like features and multiple neuromas.