The aim of the present study was to examine the association between daily omega-3 fatty acid intake and depression in Japanese cancer patients. Omega-3 fatty acid intake in 771 patients with newly diagnosed primary lung cancer was evaluated using a food-frequency questionnaire, and the prevalence of depression was examined using the cutoff values for the depression subscale included in the Hospital Anxiety and Depression Scale. After adjustment for potential confounding factors, the odds ratio (OR) for depression among patients in the highest quartile of the total eicosapentaenoic acid- (C20:5n-3) and docosapentaenoic acid (C22:6n-3)-intake group compared with patients in the lowest quartile was not significantly different. On the other hand, the OR among the highest quartile of alpha-linolenic acid (C18:3n-3) intake (adjusted OR=0.50, 95% CI: 0.31-0.71, P for trend=0.004) and the highest quartile of total omega-3 fatty acid intake (adjusted OR=0.55, 95% CI: 0.35-0.88, P for trend=0.022) were significantly different. These results suggest that total eicosapentaenoic acid and docosapentaenoic acid intake might not be associated with depression in Japanese patients with newly diagnosed lung cancer, but that alpha-linolenic acid intake and total omega-3 fatty acid intake might be.