Platelets take part in haemostasis and thrombosis, and studies have been carried out to try to understand how dietary fatty acids could reduce platelet activation and thus the risk of cardiovascular disease. Unfortunately, many of these studies had serious methodological flaws, and the shortcomings in their study designs are probably the main reason for contradictory results in humans. The evidence concerning linoleic acid is not consistent, but intervention studies show increased platelet aggregation to various agonists after high-linoleic-acid diets. On the other hand, intake of alpha-linoleic acid either has no effect or leads to decreased platelet aggregation when compared with linoleic acid. High intake of long-chain n-3 fatty acids of fish or fish oils seems to usually decrease platelet aggregation. To date, there have not been many studies on the effect of platelet aggregation of small or reasonable amounts of n-3 fatty acids.