Multiple endocrine neoplasia type III (MEN III), or MEN IIb, is a rare syndrome. We have reported 3 typical cases of MEN III since 1987. Their syndrome was characterized by striking appearance of marfanoid habitus and face, multiple mucosal neuromas affecting lips and tongue, medullary thyroid carcinoma. Their family histories were negative. Only the third case of MEN III was correctly diagnosed before operation. Medullary thyroid carcinoma was removed. The first case was followed up for 7 years without recurrence.