Dermal melanocytosis

**Definition:** The presence at birth of functional melanocytes within the dermis. Most commonly this is as a result of incomplete migration of melanocytes to the epidermis as in lumbosacral dermal melanocytosis (Mongolian spot). Less commonly it is due to circumscribed hamartomatous proliferation of melanocytes in the dermis (e.g. Naevus of Ota).