Sequence polymorphisms in a 58kb interval on chromosome 9p21 confer a markedly increased risk for coronary artery disease (CAD), the leading cause of death worldwide 1,2. The variants have a substantial impact on the epidemiology of CAD and other life?threatening vascular conditions since nearly a quarter of Caucasians are homozygous for risk alleles. However, the risk interval is devoid of protein?coding genes and the mechanism linking the region to CAD risk has remained enigmatic. Here we show that deletion of the orthologous 70kb noncoding interval on mouse chromosome 4 affects cardiac expression of neighboring genes, as well as proliferation properties of vascular cells. Chr4delta70kb/delta70kb mice are viable, but show increased mortality both during development and as adults. Cardiac expression of two genes near the noncoding interval, Cdkn2a and Cdkn2b, is severely reduced in chr4delta70kb/delta70kb mice, indicating that distant-acting gene regulatory functions are located in the noncoding CAD risk interval. Allelespecific expression of Cdkn2b transcripts in heterozygous mice revealed that the deletion affects expression through a cis-acting mechanism. Primary cultures of chr4delta70kb/delta70kb aortic smooth muscle cells exhibited excessive proliferation and diminished senescence, a cellular phenotype consistent with accelerated CAD pathogenesis. Taken together, our results provide direct evidence that the CAD risk interval plays a pivotal role in regulation of cardiac Cdkn2a/b expression and suggest that this region affects CAD progression by altering the dynamics of vascular cell proliferation.