Summary The incidence of colon cancer in industrialised countries has increased since the early 1970s. It is estimated that more than one-third of cases are associated with factors related to a Western diet. Both the type and amount of dietary fats consumed have been implicated in colon cancer aetiology. Recent studies have demonstrated that n-3 polyunsaturated fatty acids (PUFAs), commonly found in fish oil (FO), could prevent colon cancer development. Evidences show that n-3 PUFAs act at different stages of cancer development and through several mechanisms including the modulation of arachidonic acid-derived prostaglandin synthesis, and Ras protein and protein kinase C expression and activity. As a result, n-3 PUFAs limit tumour cell proliferation, increase apoptotic potential along the crypt axis, promote cell differentiation and possibly limit angiogenesis. The modulatory actions of n-3 PUFAs on the immune system and their anti-inflammatory effects might also play a role in reducing colon carcinogenesis. There remains, nevertheless, some ambiguity over the safety of n-3 PUFAs with respect to secondary tumour formation. However, it appears that n-3 PUFAs may be of use in colon cancer prevention.