We reviewed 18 cases of mucinous adenocarcinoma of the endometrium seen at this hospital during 1969-1985. Tumor histology was studied in curettage and hysterectomy material; the Hospital Tumor Registry provided follow-up data. All women were postmenopausal, 47-89 years of age, and presented with vaginal bleeding; few had abdominal pain; four of the 18 were nulliparous. Eight patients had been receiving estrogen therapy. The disease was in Stage IA in 15 patients and Stage IB in three patients. All patients had total hysterectomy and salpingo-oophorectomy; six had preoperative radium implants, and four had postoperative radium plus progesterone treatment. Histologically the tumor was grade 1 in 13 (72%) women, only five being grade 2 or 3 (28%). All tumors were positive for mucicarmine and carcinoembryonic antigen (CEA). Only two cases showed adjacent benign endometrial mucinous metaplasia. Myometrial invasion varied from 5-60% and was absent in three cases. The degree of invasion did not appear to affect the rate of recurrence. The tumor recurred 54 weeks after treatment in one of 13 patients with grade 1, in none in grade 2 and in two of two patients with grade 3 within 10 months of diagnosis. In summary, mucinous endometrial carcinoma is a rare tumor (1% of endometrial carcinomas in our hospital) of postmenopausal women; it tends to be well differentiated and has a relatively good prognosis.