OBJECTIVES The aim of the study was to investigate whether omega-3 fatty acids (n-3 FA) reduce the occurrence of restenosis after percutaneous transluminal coronary angioplasty. BACKGROUND Meta-analyses have shown significant reduction of restenosis after coronary angioplasty upon supplementation with n-3 FA. METHODS In a prospective, placebo-controlled, double-blind study, 500 patients were randomly allocated to treatment with n-3 FA (Omacor(TM), Pronova AS, Oslo, Norway) 5.1 g/day or corn oil (placebo) starting at least two weeks prior to elective coronary angioplasty. The treatment was continued until restenosis evaluation by quantitative coronary angiography after six months. Stenosis was defined as a minimal luminal diameter (MLD) <40% of the reference diameter. Successful coronary angioplasty was defined as greater than or equal to 20% acute gain in MLD and a residual stenosis <50%. Restenosis was defined as greater than or equal to 20% late loss of diameter and stenosis >50% or an increase in stenosis of 20.7 mm. Three-hundred ninety-two patients fulfilled the criteria for initial stenosis and successful coronary angioplasty, and, except four patients who died, none were lost for follow-up. RESULTS Restenosis occurred in 108/266 (40.6%) of the treated stenoses in the Omacor group and in 93/263 (35.4%) in the placebo group (odds ratio [OR] 1.25, 95% confidence interval [CI] [0.87-1.80] p = 0.21). In the Omacor group one or more restenoses occurred in 90/196 (45.9%) patients as compared with 86/192 (44.8%) in the placebo group (OR 1.05, 95% CI [0.69-1.59] p = 0.82). CONCLUSIONS Supplementation with 5.1 g n-3 FA/day for six months, initiated at least two weeks prior to coronary angioplasty did not reduce the incidence of restenosis. (C) 1999 by the American College of Cardiology.