Background The oral multikinase inhibitor regorafenib improves overall survival (OS) in patients with metastatic colorectal cancer (CRC) for which all standard treatments have failed. This study investigated regorafenib plus modified FOLFOX (mFOLFOX6) as first-line treatment of metastatic CRC. Methods In this single-arm, open-label, multicentre, phase II study, patients received mFOLFOX6 on days 1 and 15, and regorafenib 160 mg orally once daily on days 4-10 and 18-24 of each 28-day cycle. The primary end-point was centrally assessed objective response rate (ORR). Secondary end-points included disease control rate (DCR), OS, progression-free survival (PFS) and safety. Results Median overall treatment duration with any study drug was 9.9 months (range 0.6-19.6); median treatment duration with regorafenib was 7.7 months (range 0.1-19.5); six patients remained on regorafenib for more than 1 year. Fifty-three patients received at least one dose of regorafenib. ORR was 43.9 (all partial responses); DCR was 85.4 ; median OS was not reached; median PFS was 8.5 months. Treatment-emergent adverse events were experienced by all patients but were manageable with dose modifications. Conclusion Regorafenib + mFOLFOX6 as first-line treatment in patients with metastatic CRC did not improve ORR over historical controls. Regorafenib plus mFOLFOX6 did not appear to be associated with a markedly worse tolerability profile versus mFOLFOX6 alone. ClinicalTrials.gov identifier: NCT01289821.