The process of carcinogenesis is permanently one of the most interesting and significant issues for researchers in different fields of medicine. Therefore, we attempted to bring closer the problem of neoplastic transformation in the thyroid gland. This article covers the latest data about genetic factors, involved in thyroid carcinogenesis. We have presented results of the most recent studies referred to molecular biology of thyroid neoplasms. We have demonstrated not only the genetic background of cancers, derived from the thyroid follicular cell, but also genetic aspects related to medullary thyroid carcinoma and some benign thyroid lesions. The review describes DNA methylation disturbances and the mutations in thyrotropin receptor and G protein genes. Furthermore, we introduce the results of studies performed at our laboratory, concerning mutations in the following protooncogenes: RAS, RET, Trk, MET, and BRAF. Also, we present our data, regarding the loss of heterozygosity (LOH) in the short arm of chromosome 3. Additionally, we discuss overexpression of cyclin D1 gene in benign and malignant thyroid lesions. Previous studies performed at our laboratory indicate the role of IGF-I in the pathogenesis and invasiveness of thyroid cancers. The review indicates that progress in genetics of the thyroid cancer is extremely rapid.