A Gynecologic Oncology Group Phase I study was designed to evaluate the toxicity of whole abdominal radiation therapy with concurrent weekly cisplatin in patients with surgical International Federation of Gynaecology and Obstetrics (FIGO) Stage III and IV endometrial carcinoma. Cisplatin 15 mg/m2 was given once weekly during radiation therapy to the whole abdomen with a pelvic boost and optional para-aortic radiation. All eight patients received the prescribed dose of radiation therapy. Cisplatin chemotherapy was halted in one patient due to increased serum creatinine after three cycles. Acute adverse effects were within acceptable limits, with one patient admitted to the hospital after completion of treatment for diarrhea. Hematopoietic toxicity was clinically unimportant. Serious late toxicities included one radiation enteritis requiring a bowel resection and chylous ascites in one patient. There was no late renal damage reported. This regimen appears to be tolerated acutely and the late toxicities were similar to those seen with whole abdominal radiation therapy alone.