Background Supplementation with omega-3 (n-3) fatty acid or dietary fish may protect against atherosclerosis, but the potential mechanisms are unclear. Prior studies found modest triglyceride-lowering effects and slight increases in LDL (low-density lipoprotein) cholesterol. Limited evidence has examined n-3 effects on more detailed lipoprotein biomarkers. Methods and Results We conducted a study of 26 034 healthy women who reported information on fish and n-3 intake from a 131-item food-frequency questionnaire. We measured plasma lipids, apolipoproteins, and nuclear magnetic resonance spectroscopy lipoproteins and examined their associations with dietary intake of fish, total n-3, and the n-3 subtypes (eicosapentaenoic, docosahexaenoic, and α-linolenic acids). Top- versus bottom-quintile intake of fish and n-3 were significantly associated with lower triglyceride and large VLDL (very-low-density lipoprotein) particles. Fish intake, but not total n-3, was positively associated with total cholesterol, LDL cholesterol, apolipoprotein B, and larger LDL size, but only α-linolenic acid was associated with lower LDL cholesterol. Total n-3, docosahexaenoic acid, and α-linolenic acid intake were also positively associated with larger HDL (high-density lipoprotein) size and large HDL particles. High eicosapentaenoic acid intake was significantly associated with only a decreased level of VLDL particle concentration and VLDL triglyceride content. The n-3 fatty acids had some similarities but also differed in their associations with prospective cardiovascular disease risk patterns. Conclusions Higher consumption of fish and n-3 fatty acids were associated with multiple measures of lipoproteins that were mostly consistent with cardiovascular prevention, with differences noted for high intake of eicosapentaenoic acid versus docosahexaenoic acid and α-linolenic acid that were apparent with more detailed lipoprotein phenotyping. These hypothesis-generating findings warrant further study in clinical trials. Clinical Trial Registration URL: http://www.clinicaltrials.gov. Unique identifier: NCT00000479