['The balance between endothelial injury and repair in childhood is poorly understood. We examined this relationship in healthy children, in adults, and in children with familial hypercholesterolemia (FH).', 'Circulating endothelial cells (CECs) were measured as a marker of vascular injury, with vascular repair assessed by counting colony-forming units (CFUs), also known as endothelial progenitor cells.', 'CEC number increased with age. Children with FH had elevated CECs as compared with healthy children, with similar levels numerically to those found in healthy adults. CFU numbers were higher in healthy children than either healthy adults or children with FH. Endothelium-dependent vascular function, measured by flow-mediated dilatations, was positively associated with CFU number, even after adjustment for confounding risk variables.'] Are levels of circulating endothelial cells and colony-forming units influenced by age and dyslipidemia?