In humans, the population of melanocytes in the normal dermal mesenchyme is inconspicuous, and it has received little attention in the pathology literature. Indeed, the very presence of dermal melanocytes has been regarded by some as an abnormality, the result of a presumed ‘migratory arrest’ of cells targeted for the epidermis and hair follicle. However, as was mentioned in Chapter 1 (p. 6), dermal melanocytes are of significance in many animal species and, together with a small number of other pigment cell types, are responsible for the wide variety of colors of fish and reptiles; colors that have a dominant role in social signaling and mimicry. Dermal melanocytes are similarly important in some mammals. In humans, they lack an obvious function but nonetheless constitute an integral part of the normal skin. They are probably most common in the midline of the trunk, the sacrococcygeal area, and the dorsa of hands and feet.1 In some situations, such as mongolian spot and other dermal melanocytoses, hyperpigmentation of a patch of skin is caused by either an increase in pigmentation and/or an increase in the numbers of dermal melanocytes. With respect to such hyperpigmentations, the border between normality and abnormality is more or less arbitrary, because a slight increase in pigmentation of the lower back region is very common indeed.