In a pathologic review of 1224 cases of endometrial carcinoma, 1023 were confirmed cases of endometrial carcinoma. Fifty-six (5.5%) were clear-cell adenocarcinoma (CCE). Fifteen cases of "secretory carcinoma" (SCE) were examined for comparison. Fifty-five patients with CCE and all with SCE were followed for at least five years or until death. There were only 19 survivors among those with CCE. No five-year survivor subsequently died of disease. Of the 15 patients with SCE, 13 survived for five years although two additional patients died of recurrent disease at 5.4 and seven years. All survivors of CCE were Stage I patients at the time of diagnosis. All were postmenopausal, and had a median age of 67 years compared with 58 years for patients with SCE. Unlike SCE, the morphology of CCE was preserved in the subsequent hysterectomy specimen, in the recurrent disease, and in the metastases. CCE was proportionately more common in black women and the five-year survival was 12.5% as compared with 39.1% for white women. In contrast to endometrial carcinoma in general, most women who failed treatment died of disease. There was no increase in the relative frequency over the 23-year time period of the study. Age at time of diagnosis seemed to be an important prognosticator. Prognosis also correlated well with stage of disease and depth of myometrial invasion. It correlated to a somewhat lesser extent with the method of treatment and had a poor correlation with the histologic pattern or degree of cellular differentiation: however, essentially all tumors were considered to be poorly differentiated. Finally, a histologic tissue marker in the form of hyalin-like, PAS-positive, diastase-resistant bodies was found in the 64% of the women with CCE.