Medical Research Institute of Radiology, Russian Academy Forty-eight cases of familial disease (24 families) (4.3%) were identified among 1,118 patients with well-differentiated thyroid carcinoma who had been either examined or treated at the Clinic of Medical Research Institute of Radiology (1995-2004). In 86% of the study group, papillary thyroid carcinoma (PTC) was associated with tumor of the identical histological pattern while the remaining families revealed association with follicular or medullary thyroid cancer. Carcinoma inheritable from mother was the most frequent (75%). No differences in manifestation, histological pattern, stage or clinical course were established following a detailed evaluation of clinico-morphological data on 43 familial and 172 sporadic (control) cases in both groups. The analysis pointed to a significantly higher incidence of concomitant thyroid pathology in the familial thyroid cancer group. Molecular-genetic study of RET-protooncogene and gene BRAF in 6 blood samples from PTC-bearers established RET-mutation (mother and daughter) in codon 891 (exon 15) G2673A (TCG->TCA). No mutation in BRAF was found.