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Vellus hair follicle Accessory auricle Trichofolliculoma Hair nevus Abstract We present a case of hair follicle nevus, a rare hamartoma composed of vellus hair follicles. Hair follicle nevus should be differentiated from accessory auricle, trichofolliculoma and hair nevus. Masahiro Tani, MD, Department of Dermatology, Kobe University School of Medicine, 5 Kusunoki-cho, 7 chome, Chuo-ku, Kobe 650 (Japan) Hair follicle nevus [1-3] is a very rare hamartoma. A case of hair follicle nevus is here presented, and we discuss the differential diagnosis of this rare hamartoma. Case Report A 4-day-old baby boy was seen for treatment of a nodule on the left preauricular area. It had been present since birth. A physical examination revealed an elastic, soft, pedunculated, skincolored nodule, measuring 2 mm in diameter. The lesion was excised. Histopath-ologic examination showed numerous tiny but well-differentiated vellus hair follicles in the dermis (fig. 1). Some follicles were associated with small sebaceous glands, and there were a few eccrine sweat glands (fig. 2). Serial sections revealed no cartilage or smooth muscle. The overlying epidermis was almost normal. Discussion Hair follicle nevus is a rare hamartoma composed of vellus hair follicles [1-3], which is also called congenital vellus hamartoma by Headington [4]. It is usually present as a small tumor on the face at birth [2], occasionally accompanied by a few small sebaceous glands, pilar muscles and eccrine sweat apparatus [5]. Hair follicle nevus must be distinguished from accessory auricle, trichofolliculoma and hair nevus. Accessory auricle is a more complex structure, which consists not only of a pilar complex but also cutaneous appendages in different stages of development. A central plate of elastic cartilage is present in most specimens. For differential diagnosis between hair follicle nevus and accessory auricle, it is necessary to examine serial sections [6]. Trichofolliculoma usually occurs in adults. On histologic examination, the dermis contains one or several keratin-filled cysts or sinuses lined by squamous epithelium. Many small but usually fairly well-differentiated hair follicles are radiating from the wall of these cysts or sinuses. Thus, as suggested by Kligman and Pinkus [7] ‚ the cases reported by Prinz [8] and Hyman and Clayman [9] would be better