Background: To compare irinotecan with the Nordic 5-fluorouracil (5-FU) and folinic acid (FA) bolus schedule [irinotecan 180 mg/m2 on day 1, 5-FU 500 mg/m2 and FA 60 mg/m2 on day 1 and 2 (FLIRI)] or the Lv5FU2 schedule [irinotecan 180 mg/m2 on day 1, FA 200 mg/m2, 5-FU bolus 400 mg/m2 and infused 5-FU 600 mg/m2 on day 1 and 2 (Lv5FU2-IRI)] due to uncertainties about how to administrate 5-FU with irinotecan. Patients and methods: Patients (n = 567) with metastatic colorectal cancer were randomly assigned to receive FLIRI or Lv5FU2-IRI. Primary end point was progression-free survival (PFS). Results: Patient characteristics were well balanced. PFS did not differ between groups (median 9 months, P = 0.22). Overall survival (OS) was also similar (median 19 months, P = 0.9). Fewer objective responses were seen in the FLIRI group (35% versus 49%, P = 0.001) but the metastatic resection rate did not differ (4% versus 6%, P = 0.3). Grade 3/4 neutropenia (11% versus 5%, P = 0.01) and grade 2 alopecia (18% versus 9%, P = 0.002) were more common in the FLIRI group. The 60-day mortality was 2.4% versus 2.1%. Conclusions: Irinotecan with the bolus Nordic schedule (FLIRI) is a convenient treatment with PFS and OS comparable to irinotecan with the Lv5FU2 schedule. Neutropenia and alopecia are more prevalent, but both regimens are equally well tolerated. © The Author 2008. Published by Oxford University Press on behalf of the European Society for Medical Oncology. All rights reserved.