BACKGROUNDThe objective of this study was to evaluate the palliative effect of reirradiation and hyperthermia in patients with unresectable, recurrent colorectal carcinoma.METHODSThe medical records of 54 patients with unresectable, recurrent colorectal carcinoma that caused pain and who were treated with reirradiation and hyperthermia, were evaluated retrospectively. Previous radiotherapy was given up to a total dose ranging from 25–70 grays (Gy). The median interval between prior radiotherapy and reirradiation was 22 months (range, 4–97 months). The total reirradiation dose varied from 24 Gy to 32 Gy given in fractions of 4 Gy twice weekly. Three or four hyperthermia treatments were given once weekly. Toxicity was registered. The influence of World Health Organization (WHO) performance status, maximum tumor dimension, and time between first radiotherapy and reirradiation on therapeutic outcome was evaluated. The results of this study were compared with published results on patients who received radiotherapy with or without hyperthermia.RESULTSForty‐seven patients (87%) completed the planned treatment schedule. The maximum toxicity was Grade 2. All patients were evaluated for palliative effect. The median follow‐up was 10 months. A good or complete palliative effect was achieved in 72% of patients for a median duration of 6 months. Patients who had a better WHO performance status, smaller tumors, and a longer interval between first radiotherapy and reirradiation had slightly better outcomes, although none of those parameters reached statistical significance.CONCLUSIONSThe described combined treatment was feasible and well tolerated. Comparison of results from radiotherapy plus hyperthermia with results after radiotherapy alone suggested that additional hyperthermia prolonged the duration of palliation. Firm proof of the contribution of hyperthermia will require performing a Phase III study. Cancer 2003. © 2003 American Cancer Society.DOI 10.1002/cncr.11719