Nevus sebaceus of Jadassohn, or organoid nevus, is a hamartoma of the skin and its adnexae, usually seen at or shortly after birth, most commonly on the head and neck, especially the scalp. Lesions usually present as a yellowish, waxy, plaque with irregular yet well-defined margins, and alopecia. The major histopathologic features are mild papillomatous epidermal hyperplasia, superficial dermal malformed sebaceous lobules and follicular structures, and a reduction in terminal follicles, which results in the typical finding of associated alopecia.