Homeobox (Hox) genes are master regulatory genes that direct organogenesis and maintain differentiated tissue function. As HoxD3 and HoxB3 promote angiogenesis, we investigated whether endothelial cells use other Hox genes to maintain a mature quiescent phenotype. HoxD10 expression was higher in quiescent as compared to tumor-associated angiogenic endothelium. Microarray analysis of HoxD10-overexpressing endothelial cells revealed a pattern of gene expression consistent with a nonangiogenic phenotype. Moreover, sustained expression of HoxD10 impaired endothelial cell migration and blocked angiogenesis induced by basic fibroblast growth factor and vascular endothelial growth factor in the chick chorioallantoic membrane in vivo. HoxD10-overexpressing human endothelial cells also failed to form new vessels when implanted into immunocompromised mice. These results indicate a role for HoxD10 in maintaining a nonangiogenic state in the endothelium.