The cytogenetic results from a series of 113 thyroid hyperplasias and adenomas are reported; 15 showed clonal karyotypic alterations. In addition to a group showing translocations involving 19q13, another subset of lesions characterized by polysomies can be found. Based on our own cases belonging to this subset and a review of the cases reported in the literature, we conclude that the characteristic feature of this group is a sequence that always starts with trisomy 7, but that sometimes even leads to chromosome numbers in the hypertriploid range. This subset of thyroid tumors may be an example of a more common genetic pathway in human solid tumors.