The objective of this study was to determine the effects of prescription omega-3 (n-3) fatty acid ethyl esters (Omacor®) on blood pressure, plasma lipids, and inflammatory marker concentrations in patients awaiting carotid endarterectomy. Patients awaiting carotid endarterectomy (n = 121) were randomised to Omacor® or olive oil as placebo (2 g/day) until surgery (median 21 days). Blood pressure, plasma lipids, and plasma inflammatory markers were determined. There were significant decreases in systolic and diastolic blood pressure and in plasma triglyceride, total cholesterol, low density lipoprotein-cholesterol, soluble vascular cellular adhesion molecule 1, and matrix metalloproteinase 2 concentrations, in both groups. The extent of triglyceride lowering was greater with Omacor® (25%) compared with placebo (9%). Soluble E-selectin concentration was significantly decreased in the Omacor® group but increased in the placebo group. At the end of the supplementation period there were no differences in blood pressure or in plasma lipid and inflammatory marker concentrations between the two groups. It is concluded that Omacor® given at 2 g/day for an average of 21 days to patients with advanced carotid atherosclerosis lowers triglycerides and soluble E-selectin concentrations, but has limited broad impact on the plasma lipid profile or on inflammatory markers. This may be because the duration of intervention was too short or the dose of n-3 fatty acids was too low.