Acanthosis nigricans is characterised by dark, thick, velvety skin in body folds and creases. It is most commonly encountered in association with obesity and type 2 diabetes though may be a component of a number of genetic syndromes. Hyperinsulinaemia and insulin resistance are important underlying factors. Acanthosis nigricans may rarely be due to underlying malignancy (paraneoplastic acanthosis nigricans).