Type 2 diabetes mellitus (T2DM) is accompanied by dysfunctional high-density lipoprotein (HDL) and this is characterized by alterations in its composition and structure compared with HDL from normal subjects (N-HDL). HDL from diabetic subjects (D-HDL) has a diminished endothelial protective capacity including reducted ability to exert antioxidative activity, stimulate endothelial cell (EC) production of nitric oxide (NO) and endothelium-dependent vasomotion, promote endothelial progenitor cell (EPC)-mediated endothelial repair. In addition, D-HDL promotes EC proliferation, migration and adhesion to the matrix. The present review provides an overview of these effects of diabetic HDL on EC function, as well as the possible changes of D-HDL structure and composition which may be responsible for the diminished endothelial protective capacity of D-HDL.