Despite the fact that adenocarcinoma of the endometrium is currently the most common gynecologic malignancy in the United States, few chromosomal studies have been done to date characterizing this disease. HEC-1A, a cell line used by many laboratories as a reference cell line for endometrial carcinoma, has never been subjected to definitive karyotyping. For this reason, with the use of improved banding techniques, this has now been accomplished, and several consistent abnormalities have been identified. There was a marker chromosome formed from an insertion of 2q21, probably representing an insertion of the lacking chromosome 14. In addition, there was a translocation to the telomeric region of 1p; and trisomies of 3, 7, and 17. Many of these abnormalities are known to consistently be associated with other primary malignancies. In addition, the chromosomes in which trisomy is noted carry genes associated with epidermal growth factor and estrogen receptors, which also bear marked homology to known oncogenes. It would appear that further detailed studies of various grades and stages of endometrial carcinoma, as well as histologic types and "precursor lesions," may lead to an understanding of those chromosomal changes associated with disease initiation and progression.