BACKGROUND Adjuvant postoperative treatment with 5-fluorouracil (5-FU) and leucovorin in curatively resected stage III colon cancer significantly reduces the risk of cancer recurrence and improves survival. The impact of continuous 5-FU with and without leucovorin on survival and tumor recurrence was analyzed in this study compared with the effects of bolus 5-FU/leucovorin. METHODS Patients with a curatively resected UICC stage III colon cancer were stratified according to T, N and G category and randomly assigned to receive one of the three adjuvant treatment schemes: 5-FU 450 mg/m2 and leucovorin 100 mg/m2 x 5 days every 4 weeks; six cycles, arm A; 24-h infusion of high-dose 5-FU/leucovorin 2,600 mg/m2 and 500 mg/m2, two cycles of six applications, arm B; 24-h infusion of high-dose 5-FU 2,600 mg/m2, two cycles of six applications, arm C. RESULTS One hundred and forty-five patients enrolled into this study were eligible. To date, 28 patients have died; 9 on arm A, 11 on arm B, and 8 on arm C (P was nonsignificant). After a median follow-up time of 45 months, there was no statistical difference in survival and tumor recurrence between the three treatment arms. Adjuvant treatment in all arms was generally well tolerated; only a minority of patients experienced grade 3 and 4 toxicities. CONCLUSIONS There is no statistical difference in efficacy and toxicity in patients receiving either high-dose 5-FU with or without leucovorin or the standard 5-FU bolus regime after a curative resection of a stage III colon cancer.