The prognostic value of primary tumour location for overall survival, which is well established in patients with metastatic colorectal cancer, was investigated in 1,869 patients with stage III nonmetastatic colorectal cancer receiving adjuvant FOLFOX (5-fluorouracil, leucovorin and oxaliplatin) with or without cetuximab. In the whole population, a right-sided tumour location was associated with shorter survival after relapse and shorter overall survival than left sidedness, but was not prognostic for disease-free survival (DFS). In patients with RAS-mutant disease, DFS was more favourable in those with right-sided versus left-sided tumours, and the opposite pattern was observed in those with both wild type RAS and BRAF; in addition no differences related to microsatellite stability status or cetuximab treatment were observed.