Multiple endocrine neoplasia type 2 (MEN 2) is a hereditary syndrome which can present itself either in a familial form, characterized by a dominant pattern of inheritance, or in a sporadic form. It can be subdivided into multiple endocrine neoplasia type 2A (MEN-2A), multiple endocrine neoplasia type 2B (MEN-2B), and familial medullary thyroid carcinoma (FMTC).1-3 Among these conditions, MEN-2B, which has an extremely low rate of incidence, is the most severe form. Its clinical presentation includes C-cell hyperplasia or medullary thyroid carcinoma, pheochromocytoma, ganglioneuromatosis, accompanied with Marfanoid body habitus.4-8 Using the methods of single-strand conformational polymorphism (SSCP) and direct gene sequencing, Hofstra et al9 and Calson et al10 showed for the first time that MEN-2B is associated with a mutation in the RE arranged during transfection (RET) proto-oncogene, which is a receptor-type tyrosine kinase. The RET gene is located in the centromeric region of chromosome 10q11.2, and consists of 21 exons. Over 95% of MEN-2B patients have a specific point mutation at codon 918 in exon 16 of RET, resulting in the replacement of methionine with threonine [918Met(ATG)→Thr(ACG)].11-16 Although there have been many reports on the gene mutation associated with MEN-2B,17-19 there has been no previous reports on similar genetic studies in Chinese patients. In this study, we identified a MEN-2B Chinese patient and tried to establish the relationship between an RET gene mutation and the onset of MEN-2B, in order to further understand the hereditary characteristics of this disease and a basis for early diagnosis and early intervention.