Endometrial metaplasia is a complex group of epithelial proliferations. The relationship of metaplasia, other than squamous metaplasia, to endometrial adenocarcinoma has not been clearly established. Between 1969 and 1979, 183 patients diagnosed as having Stage I endometrial adenocarcinoma (according to International Federation of Gynecology and Obstetrics) were treated at the University of Virginia Medical Center. Sixty of the patients were treated with hysterectomy without preoperative irradiation. A histopathologic review was performed without knowledge of the clinical outcome and subsequent clinicopathologic correlations were analyzed. On review, 32/60 had carcinoma without metaplasia and 15/60 had both carcinoma and metaplasia. Thirteen of the 60 patients were judged not to have cancer: 12 had both hyperplasia and metaplasia and one had hyperplasia without metaplasia. None of the 12 patients reclassified as having metaplasia had a recurrence or died of endometrial carcinoma. Patients with both metaplasia and carcinoma were significantly younger than patients with only carcinoma and the associated carcinomas were more frequently well differentiated.