CVD refers to disease of the heart and blood vessels and is the leading cause of mortality in Ireland. CVD Begins in childhood and adolescence due primarily to exposure to lifestyle mediated risk factors . Endothelail dysfunction, induced by CVD risk factors, is one of the earliest events in the development of CVD and precedes structural changes in the artery walll such as intima media thickness. Exercise training has been shown to restrore endothelial function (EF), decrease carotid intima media thickness (cIMT) and improve CV risk profile in obese children. There is currently no research that has examined subclinical atherosclerotic CVD in asympomatic adolescents with low and high cardiorepsiratory fitness (CRF). This study compared CVD risk factors, cIMT and EF in adolescent boys with low and high CRF and examined the relation between CRF and cIMT and CRF and FMD in asympomatic adolescent boys. It was hypothesised that boys with a high CRF would have a healthier CV profile and that there would be an inverse relation between CRF and cIMT and CRF and EF.