Background/Aim: Associations between dietary intake of various fats and specific K-ras mutations in colorectal cancer (CRC) were investigated within the framework of the Netherlands Cohort Study on diet and cancer (NLCS). Methods: After 7.3 years of follow-up and with exclusion of the first 2.3 years, 448 colon and 160 rectal cancer patients and 3048 subcohort members (55-69 years at baseline) were available for data-analyses. Mutation analysis of the K-ras gene was performed on all archival colon and rectal adenocarcinoma specimens. Case-cohort analyses were used to compute adjusted incidence rate ratios (RR) and 95% confidence intervals (CI) for colon and rectal cancer cases and for K-ras mutation subgroups. Results: Intake of total, saturated and mono-unsaturated fat was not significantly associated with colon or rectal cancer. High intake of dietary poly-unsaturated fat and, specifically, linoleic acid is associated with an increased risk of mutated K-ras colon tumours. The RRs for one standard deviation of increase of poly-unsaturated fat and linoleic acid were 1.21 (95% CI 1.05-1.41) and 1.22 (95% CI 1.05-1.42), respectively and similar associations were observed for both G>A transitions and G>T or G>C transversions in the colon. In contrast, no significant associations were observed with rectal cancer risk, overall nor with specific K-ras mutation status. Conclusions: A high intake of poly-unsaturated fat, in particular linoleic acid, may be an important dietary risk factor for K-ras mutated colon tumours, possibly by generating G>A transitions or G>T or G>C transversions in the K-ras oncogene.