Résumé : Background. There is conflicting evidence on the efficacy of regional adjuvant chemotherapy, via portal-vein infusion (PVI), after resection of colorectal cancer. We undertook a randomised controlled multicentre trial to investigate the efficacy of PVI (500 mg/m2 fluorouracil plus 5000 IU heparin daily for 7 days). Methods. 1235 of about 1500 potentially eligible patients were randomly assigned surgery plus PVI or surgery alone (control). The patients were followed up for a median of 63 months, with yearly screening for recurrent disease. The primary endpoint was survival; analyses were by intention to treat. Findings. 619 patients in the control group and 616 in the PVI group met eligibility criteria. 164 (26%) control-group patients and 173 (28%) PVI-group patients died. 5-year survival did not differ significantly between the groups (73 vs 72%; 95% CI for difference -6 to 4). The control and PVI groups were also similar in terms of disease-free survival at 5 years (67 vs 65%) and the number of patients with liver metastases (79 vs 77%). Interpretation. PVI of fluorouracil, at a dose of 500 mg/m2 for 7 days, cannot be recommended as the sole adjuvant treatment for high-risk colorectal cancer after complete surgical excision. However, these results cannot eliminate a small benefit when PVI is used at a higher dosage or in combination with mitomycin.