Mechanisms underlying the yellow color of these lesions have been addressed in Chap. 3, dedicated to macules. Upon initial clinical evaluation, yellow circumscribed lesions can immediately be differentiated from a more diffuse yellow dyschromia (such as carotenoid pigmentation, certain drug intoxications or, rarely, diffuse plane xanthomatosis). In the case of yellow circumscribed lesions, keratoses are easily identified by the rough nature of the primary lesion. Although purpura evolves through a transient yellow coloration, it is easily diagnosed through history taking and the presence of associated lesions. When diagnosing other yellow infiltrated lesions, skin biopsy is usually mandatory, as well as special coloration techniques such as orcein staining, which allows visualization of elastic fibers and thioflavin T for identification of amyloid deposits. Immunohistochemistry techniques are also required for characterizing either a lymphomatous or histiocytic infiltrate. Certain yellow palpable lesions are the morphological expression of pseudoxanthoma elasticum. This rare disorder of the elastic tissue may explain an early atheromatosis and thus explain so far unresolved episodes of coronaropathy and strokes in a young patient. In neonates, the most common causes of a yellow papule or plaque are sebaceous hamartoma, juvenile xanthogranuloma, and mastocytoma.