Baseline blood levels of long-chain n-3 fatty acids were very significantly inversely related to the risk of sudden death. As compared with the men whose blood levels of the n-3 fish oil fatty acids were in the lowest quartile, the relative risk of sudden death was significantly lower among men in the third quartile (relative risk ratio, 0.28) and in the fourth quartile (0.19). The 72 and 81% relative risk reductions are the largest beneficial cardiac effects of the n-3 PUFA so far reported in humans.