Acanthosis nigricans is a velvety thickening of the epidermis that primarily affects the axillae, posterior neck fold, flexor skin surfaces, and umbilicus, and infrequently is diffuse with involvement of the mucosal surfaces. It is increasingly seen in children and adolescents who are obese, and can serve as a cutaneous marker of insulin resistance and malignancy. Although malignancy-associated acanthosis nigricans is rare in the pediatric population, one need be concerned about its association with certain pediatric syndromes. More importantly, insulin resistance itself can also represent a threat to life. We review this important disorder.