A diabetic foot ulcer is an open sore that develops on the foot, most often on the bottom of the foot or the tips of the toes. They affect roughly 15% of people with diabetes. Because diabetic neuropathy reduces sensation, many patients don't notice an ulcer until it has already become infected. Left untreated, ulcers can progress to osteomyelitis (bone infection) and, in severe cases, may require amputation. Early diagnosis and specialist care dramatically improve outcomes.