Clinical manifestations of the insulin resistance syndrome are accompanied by endothelial dysfunction at the level of conductance and resistance vessels. Other conditions, such as smoking, also associated with endothelial dysfunction, exhibit insulin resistance too. Hypercholesterolaemia, in contrast, despite being the classical disease of endothelial dysfunction, is not associated with insulin resistance. Furthermore, only in insulin-resistant diseases, markers of microvascular alteration, such as microalbuminuria or increased plasma concentrations of von Willebrand factor, are found. At capillary sites, in contrast, transendothelial transport of both insulin and glucose takes place. These transport processes are thought to contribute to overall insulin sensitivity. In this article, I not only hypothesize but also summarize existing experimental and clinical evidence that a distinct capillary endothelial dysfunction is closely involved in the insulin resistance syndrome.