BACKGROUND: This randomized study targeted a comparison of the effect of 3-year diet counselling or omega-3 polyunsaturated fatty acid (PUFA) supplementation (2.4 g/day) on the progression of atherosclerosis in carotid arteries and on finger pulse wave propagation. METHODS: Measurements were assessed by high-resolution B-mode ultrasound and a photopletysmographic finger pulse-sensor, respectively. Altogether, 563 elderly men with long-standing hyperlipidaemia were randomized into four groups: controls (no dietary counselling and placebo); dietary counselling (and placebo); omega-3 PUFA supplementation (no dietary counselling); dietary counselling and omega-3 PUFA supplementation. RESULTS: In the diet only group, the carotid intima-media thickness increase (0.929 to 0.967 mm) was significantly less than in the control group (0.909 to 0.977 mm), (P = 0.018). Significant increase in carotid plaques score and plaques area were observed in all four groups, but without between group differences. Changes in carotid intima-media thickness and in high-density lipoprotein-cholesterol were negatively correlated (adjusted P < 0.001). Pulse wave propagation time decreased significantly in the control group (206 to 198 ms; P = 0.002), reflecting reduced arterial elasticity. In the group receiving omega-3 PUFA only, pulse wave propagation time increased significantly when compared with the control group (P = 0.013). CONCLUSION: Reduced progression in carotid intima-media thickness was observed after dietary counselling, whereas omega-3 PUFA supplementation imposed a favourable effect on arterial elasticity.