Background: Phytanic acid, a fatty acid predominantly obtained from foods high in ruminant fat, may have a biological role in the up-regulation of the protein α-methylacyl-coenzyme A racemase, which is overexpressed in prostate cancer tissue. Objective: This study aimed to examine the association between plasma concentrations of phytanic acid and subsequent risk of prostate cancer. Design: Within the European Prospective Investigation into Cancer and Nutrition cohort, 566 incident prostate cancer cases from Germany, Greece, Italy, the Netherlands, Spain, and the United Kingdom were individually matched to 566 controls by study center, age at recruitment, and time of day and duration of fasting at blood collection. Phytanic acid concentrations were measured by using a gas chromatography-mass spectrometry assay. Results: In controls, plasma phytanic acid concentration was strongly correlated with dairy fat intake (r = 0.49, P 3 h) at blood collection, the odds ratio for prostate cancer was 1.27 (95% CI: 1.01, 1.60; P for trend = 0.04). Conclusion: Plasma phytanic acid concentration is significantly associated with intake of dairy fat but not with overall risk of prostate cancer in this European population. © 2010 American Society for Nutrition.