One hundred patients with potentially curable squamous cell carcinoma of the esophagus were treated using a combination of external beam radiation, medium-dose intraluminal brachytherapy (ILBT), and 5-fluorouracil infusion (as a radiosensitizer) from January 1990 to December 1993. The main objective was to determine late toxicity and optimization of the dose of intraluminal radiation. All patients had external radiation of 50 Gy over 5 1/2 weeks, followed by ILBT of 20 Gy for 50 patients (group 1) and 15 Gy for a subsequent 50 patients (group 2), using a dose rate of 315-330 cGy/h with the prescription at 1 cm off axis. The 5-fluorouracil infusion was 500 mg/m2 administered 12 h prior to ILBT. The treatment-related complications among groups 1 and 2 were strictures 24% vs. 8% (p = 0.029), ulceration 30% vs. 28% (p = 0.8), and tracheoesophageal fistulae 12% for both groups. The overall survival for groups 1 and 2 was 8% and 23% at 5 years. The development of life-threatening complications is a major concern and extreme caution is urged before selecting patients for a combination of ILBT and 5-fluorouracil treatment.