Necrobiosis lipoidica and granuloma annulare are granulomatous skin conditions that have been traditionally associated with diabetes mellitus, although recently the strength of association has been questioned. In the first section of this two-part article, we describe the suggested aetiology, clinical features, histology and treatment of necrobiosis lipoidica. It is found in 0.3% of patients with diabetes, but has also been reported with other systemic conditions. Clinically it appears as a waxy, atrophic, yellowish plaque with overlying telangiectasia and a brown border. Although usually asymptomatic, it may be extremely painful, especially if ulcerated. Squamous cell carcinoma has occasionally been reported with longstanding lesions. Treatment is often difficult: numerous topical and systemic agents have been employed, but evidence is limited to small case series and individual case reports. Br J Diabetes 2016;16:6-9