Gruppo Italiano per lo Studio della Sopravvivenza nell'Infarto Miocardico (GISSI)-Prevenzione was the first large randomized trial to produce evidence that a pharmaceutical preparation of highly purified omega-3 polyunsaturated fatty acids (PUFAs), administered as an adjunct to other accepted interventions, had a favorable effect on hard clinical end-points in post-myocardial infarction patients. Much of the 20% all-cause mortality benefit recorded during the study could be attributed to a 45% reduction in sudden death--a fatal outcome that traditionally has proved resistant to medical intervention. These results were obtained with an omega-3 PUFA dose of 1 g/day, which is much lower than was routinely being used at the time the study was initiated (e.g. 4 g/day for hypertriglyceridemia). One consequence of this low-dose regimen was that the tolerability profile of omega-3 PUFAs during GISSI-Prevenzione was considered highly satisfactory, with low adverse event incidence rates and low rates of discontinuation due to adverse events. Time-course analysis established that much of the survival benefit of omega-3 PUFA treatment in GISSI-Prevenzione was realized during the early months of the trial. The beneficial effects of omega-3 PUFA treatment were observed on top of standard, secondary pharmacological prevention therapy like anti-platelet agents, statins, beta-blockers and angiotensin-converting enzyme (ACE) inhibitors. The benefits of omega-3 PUFA therapy were also apparent in patients at all standards of adherence to a healthy diet and may have been augmented in patients with the best dietary profile. Patients with diabetes mellitus (approximately 15% of the study cohort) appeared to benefit from omega-3 PUFAs to at least the same extent as the general study population; the treatment effect on sudden death was progressively more pronounced as left ejection fraction declined. Cost-effectiveness analyses undertaken from a third-party payer perspective for Italy revealed that the cost of low-dose treatment with highly purified omega-3 PUFAs was approximately Euro 25,000 per life-year gained.