We report a case of diabetic muscle infarction in a 22-yr-old woman, with an 11-yr history of poorly controlled Type 1 diabetes complicated by laser-treated pre-proliferative retinopathy, macroalbuminuria and severe autonomic neuropathy, also affected by IgA deficiency, autoimmune hypothyroidism, coeliac disease and polygenic familiar hypercolesterolaemia. She was admitted to our Hospital for pain to the left thigh hindering her from walking. The pain had appeared without trauma about 2 months before admission, and worsened progressively in spite of anti-inflammatory drugs. Clinical picture (localised tender mass without skin signs of inflammation in an afebrile patient) and laboratory data (erythrocyte sedimentation rate 113 mm in 1 hr, fibrinogen 635 mg/dl) suggested the diagnosis of diabetic muscle infarction. Magnetic resonance imaging (MRI) confirmed this hypothesis showing a hyperintense area in T2-weighted sequences at adductor muscle group with enhancement after intravenous contrast. Symptoms subsided over the following 4 weeks after bed rest, analgesics, aspirin and a good glycaemic control. The 3-month follow-up MRI showed total recovery. At hospital admission, the patient presented a very poor glycaemic control (HbA1c 15.5%). After discharge, she started--in order to avoid the weight gain associated with intensive insulin therapy--a daily intense isometric training, undergoing frequent hypoglycaemic episodes. In a few months, in spite of repeated laser treatment, retinopathy progressed to the proliferative stage with bilateral vitreous haemorrhages and visual acuity decreased dramatically notwithstanding vitrectomy. This case confirms the association of diabetic muscle infarction with poorly controlled long-standing diabetes with microvascular complications, suggests the possible role of autoimmunity, and underlines the risk of repeated hypoglycaemic episodes and isometric exercise in the progression of pre-proliferative retinopathy.