Although the simultaneous presentation of endometrial and ovarian carcinomas of the endometrioid type is well described, little is known about a similar phenomenon involving the endometrium and fallopian tube (FT). We present the clinicopathologic features of 13 such cases seen in the Department of Pathology at The University of Texas M.D. Anderson Cancer Center over an 8 year period (1995 to 2002). FT tumors that could have represented luminal extension of the endometrial carcinoma or that represented an unequivocal metastasis to the FT were excluded. The patients' ages ranged from 34 to 77 years (median 54). The most common symptom was abnormal uterine/vaginal bleeding (11) and all of the patients were considered overweight or obese (mean body mass index was 41). The size of the endometrial carcinomas ranged from 0.3 to 8 cm. According to the FIGO grading of the endometrial endometrioid carcinomas, the cases were distributed as follows: Grade 1 (3) and Grade 2 (10). In 2 cases, there were also small areas of other histologic types, papillary serous carcinoma (1 case), and papillary endometrial carcinoma of intermediate grade (another case). The size of the fallopian tube carcinomas ranged from 0.2 to 17.5 cm. Seven of these tumors were located in the distal/fimbriated end of the FT. There was bilateral involvement in 2 cases. Three of the FT tumors were in situ. The grades of the fallopian tube carcinomas were as follows: Grade 1 (2), Grade 2 (6), and Grade 3 (2). In situ components were seen in all cases. One fallopian tube carcinoma was mixed with serous carcinoma. In 4 cases, there was also an endometrioid carcinoma involving the ovary, all of them with an intact ovarian capsule. Patients were treated as follows: total abdominal hysterectomy and bilateral salpingo-oophorectomy (TAH/BSO) (4), TAH/BSO/chemotherapy (chemo) (4), TAH/BSO/radiation (3), and TAH/BSO/chemo/radiation (2). Follow-up ranging from 6 to 54 months was available in 10 patients: 1 patient died of disease (at 38 mo), 1 patient is alive with disease (at 9 mo), 7 patients have no evidence of disease (6 to 54 mo), and 1 patient died of metastatic endometrial carcinoma (at 9 mo). Simultaneous endometrioid carcinomas of the uterus and FT are unusual and occur primarily in obese perimenopausal women. The tumors are predominantly well or moderately differentiated with dissimilar endometrial and FT grades. The FT carcinoma is usually unilateral and located at the distal end of the tube.