To determine the relative risk of complications in treating ankle fractures in patients with diabetes, we compared the results of the management of displaced malleolar fractures in 26 patients with those of a matched group of non-diabetic patients, using a case-controlled study. The groups were matched for patient age, fracture type and treating surgeon. The incidence of significant complications in diabetic patients was 42.3%. By contrast, there were no complications in the matched group of non-diabetic patients. Of 19 diabetic patients treated surgically, six developed major complications including one case of malunion, one of necrosis of the wound edge requiring a flap, and two of deep sepsis. Two patients required amputation and both died. Diabetic patients with displaced ankle fractures treated non-operatively had a high incidence of loss of reduction and malunion but these caused few symptoms. In these patients, non-operative management may be preferable in view of the high risks of major complications after surgery and the acceptance of malunion by the older patient with lower demands.