Lightly pigmented thin plaques formed by closely apposed papules, initially and sometimes only tiny, but sometimes large and polypoid. The plaques are often traversed by skin folds. There is a predisposition for intertriginous areas. The condition is due to metabolic disturbances, such as endocrine disorders, obesity, or malignancy. Medications that influence insulin metabolism may rarely be implicated (i.e., corticosteroids, estrogen, protease inhibitors, somatotrophin, and niacin). So-called malignant acanthosis nigricans is a misnomer, as it is not malignant per se, but due to an underlying malignancy. In such cases, the condition can be the presenting sign, or can follow detection of the tumor. A variety of tumors can cause acanthosis nigricans, but gastric adenocarcinoma is the most common. The clinical and pathologic appearance of the condition is identical, regardless of cause, but a generalized distribution or rapid onset can point to an underlying tumor. In this setting, velvety thickening may occur in dermatoglyphics of palmar skin, referred to as tripe palms or “acanthosis palmaris.” Tripe palms may be observed independently or in association with acanthosis nigricans. Whether this is a disease sui generis or a unique variant of acanthosis nigricans remains unclear. The histopathologic image of acanthosis nigricans shows narrow papillations with thin suprapapillary plates.