Intraoperative radiotherapy (IORT) is being used with increasing frequency in many institutions in the United States but little is known about the surgical complication rates. The Radiation Therapy Oncology Group initiated three prospective studies in IORT in 1986 and we report here the experience in advanced malignancies of the stomach, pancreas, and rectum. The incidence and nature of major surgical complications were reviewed and presented with their implications in regard to future IORT trials. Two hundred twenty-seven patients were entered on three studies by 20 participating institutions between 1985 and 1989. One hundred twenty-nine patients received IORT while 98 patients were found to have too advanced disease to be benefited by IORT and underwent palliative surgical procedures only. IORT doses ranged from 12-22 Gy and bowel anastomoses were not irradiated. Wound infection in the IORT group was 6% vs. 2% in the non-IORT patients but this was not significant at the P = 0.05 level. Other complications included anastomotic leak (n = 5), operative bleeding (n = 10), pancreatitis (n = 2), and were not statistically different in the IORT and non-IORT groups. The mortality rate for the IORT and non-IORT groups combined was 1.8%. This large multi-institutional experience in patients with advanced malignancy demonstrates that patients receiving IORT do not have a higher surgical complication rate than those not receiving IORT. Long-term survival data await the implementation of Phase III trials in advanced intra-abdominal malignancy.