Terra firma-forme dermatosis (TFFD), also known as Duncan' dirty dermatosis, is a keratinization disorder that is characterized by velvety, dark brown-blackish patches, and plaques and is not associated with systemic diseases. The lesions rarely show a verrucous or reticulate appearance. Especially, in children and adolescents, neck, face, torso, and ankles are the most frequently affected areas. TFFD is a condition that should be suspected in children and adolescents that cannot be cleaned with soap, especially if the neck area looks dirty. In this article, we report 3 cases with a diagnosis of TFFD resembling acanthosis nigricans. TTFD should be included in the differential diagnosis of adolescent cases presenting with hyperpigmented patches and plaques, especially in intertriginous areas such as the neck.