High lipoprotein(a) (Lp(a)) levels are a major risk factor for the development of atherosclerosis. The risk of elevated Lp(a) concentration is increased significantly in patients who also have high levels of low density lipoprotein (LDL) cholesterol. To test the hypothesis that increased plasma levels of Lp(a) may enhance the development of atherosclerosis in the setting of hypercholesterolemia, we generated Watanabe heritable hyperlipidemic (WHHL) transgenic (Tg) rabbits expressing human apolipoprotein(a) (apo(a)). We report here that Tg WHHL rabbits developed more extensive advanced atherosclerotic lesions than did non-Tg WHHL rabbits. In particular, the advanced atherosclerotic lesions in Tg WHHL rabbits were frequently associated with calcification, which was barely evident in non-Tg WHHL rabbits. To investigate the molecular mechanism of Lp(a)-induced vascular calcification, we examined the effect of human Lp(a) on cultured rabbit aortic smooth muscle cells and found that smooth muscle cells treated with Lp(a) showed increased alkaline phosphatase activity and enhanced calcium accumulation. These results demonstrate for the first time that Lp(a) accelerates advanced atherosclerotic lesion formation and may play an important role in vascular calcification.