Adenocarcinoma of the pancreas is an extremely malignant neoplasm with a particular propensity to spread to the liver. In an effort to combine chemotherapy with high-dose local irradiation plus a modest dose of irradiation to suspected (subclinical) hepatic metastasis, patients with unresectable pancreatic carcinomas with no known distant metastasis were treated on a prospective multi-institutional Radiation Therapy Oncology Group (RTOG) Phase I/II trial. High total dose continuous radiation therapy to the pancreas (6120 cGy in 34 fractions over 7 weeks) and simultaneous prophylactic hepatic irradiation (PHI, 2340 cGy in 13 fractions for the last 2.5 weeks) were combined with administration of 5-fluorouracil 1000 mg/m2/day (maximum, 1500 mg) by intravenous continuous infusion for 5 days starting on day 1 and repeated on day 30 for 5 days, followed by a dose of 600 mg/m2 as a weekly bolus injection starting during week 9 for 6 months. In 18 months, 81 patients were enrolled in the study; 79 were evaluable with a minimum potential follow-up of 8.2 months. The patients ranged in age from 32 to 75 years (median, 64 years). Karnofsky performance status was 80 to 100 in 74% of patients. The tumor was confined to the head of the pancreas in 72% of patients. The planned radiation therapy for the pancreas was completed in 87% of patients, 80% received the planned PHI, and 85% completed the first two cycles of chemotherapy. Seventy-five percent of patients completed both treatments according to the protocol. Most patients who did not complete both treatments had tumor progression or refused additional therapy. During all cycles of chemotherapy and radiation therapy, 2 patients died of complications (Grade 5, 1 hepatic and 1 infection), 9 had life-threatening reactions (Grade 4, 7 hematologic, 1 neurologic, and 1 mucositis), and 31 patients had severe effects (Grade 3) according to the RTOG toxicity scale. Overall hepatic metastasis was documented in 32% (13% as the first site of failure), persistent or progressive pancreatic tumor was evident in 73%, and abdominal and extra-abdominal spread were reported in 27% and 8% of patients, respectively. Eighty percent (63 patients) died (median survival, 8.4 months). Although this study suggests that PHI may reduce the frequency of hepatic metastasis, failure to control the primary tumor and intraabdominal spread remain overwhelming.