Abstract： Background:Familial nonmedullary thyroid carcinoma (FNMTC) is a variant ofnonmedullary thyroid carcinoma(NMTC) with particular clinicopathologic features.In recent years,a number of studies have shown that FNMTC is more invasive than sporadic NMTC(SNMTC).The purpose of this study was to explore the differences in clinicopathologic features of FNMTC between different types of families and to determine in which of these families more invasive FNMTC occurred.Methods:We retrospectively reviewed all patients with thyroid carcinoma admitted to Peking Union Medical College Hospital from January 2009 to July 2013 in the database.Of all 2000 cases,55 met the inclusive criteria for FNMTC and were studied.There are two different grouping methods.The first is that all samples were allocated to families with three or more first-degree relatives affected (FNMTC-3 group) and families with only two affected first-degree relatives (FNMTC-2 group).The second is that all patients were divided into families with three or more affected first-degree relatives over two generations (FNMTC-3-2 group) and the other families.We compared the clinicopathologic features such as sex,age,tumor size,multifocality,location,complications by thyroiditis,complications by benign thyroid nodules,surgical procedure,capsule invasion,histological type,lymph node metastases,tumor node metastasis stage,and BRAF mutation between FNMTC-2 group and FNMTC-3 group.We also made the same comparison between FNMTC-3-2 group and other families.Results:No pronounced differences in clinicopathological features were present between FNMTC-2 group and FNMTC-3 group.The proportion of FNMTC-3-2 group aged ＜45 years was significantly higher than that in the other families (58.8％ vs.26.3％,P =0.021).A similar difference was found in the proportion of lymph node metastasis (64.7％ vs.34.2％,P =0.035).Conclusions:FNMTC-3-2 is more invasive than the other families.Early screening and positive treatment for members of these families are recommended.