Acanthosis nigricans (AN) can be a highly significant cutaneous finding and is usually unrelated to cancer. It is most often evident as velvety thickening of axillae, posterior neck fold, flexor skin surfaces and umbilicus. It is common in obesity, which is seen increasing in children and adolescents, and can serve as a cutaneous marker of insulin resistance. It is most often associated with hyperinsulinemia, which may result from insulin receptor gene defects causing insulin resistance, and less frequently due to mutations in fibroblast growth factor receptors. In this work non malignancy-associated AN types will be emphasized, particularly the association of AN with insulin-resistance, itself a potential threat to life.