Significance Diabetic foot ulcerations (DFUs) represent a major medical and economic problem with still-unclear pathogenic mechanisms. The Notch pathway plays a pivotal role in cell differentiation, proliferation, and angiogenesis, processes that are profoundly disturbed in diabetic wounds. Notch signalling is activated upon interactions between membrane-bound Notch receptors (Notch 1–4) and ligands (Jagged 1–2 and Delta-like 1, 3, 4). Here, we report that a specific positive Delta-like 4–Notch1 feedback loop is activated by high glucose levels and specifically impairs wound healing in diabetes. Local inhibition of Notch signalling in experimental wounds using chemical and genetic approaches markedly improves healing exclusively in diabetic, but not in nondiabetic, animals, making Notch1 signalling an attractive locally therapeutic target for the treatment of DFUs.