A clinical entity called "the epidermal nevus syndrome" does not exist. Rather, there are various epidermal nevus syndromes that can be distinguished by clinical, histopathological, and genetic criteria. In this review, five distinct epidermal nevus syndromes, recognizable by different types of associated epithelial nevi, are described. The Schimmelpenning syndrome is characterized by a sebaceous nevus associated with cerebral anomalies, coloboma, and lipodermoid of the conjunctiva. By contrast, cataracts are a prominent feature of the nevus comedonicus syndrome. The pigmented hairy epidermal nevus syndrome includes Becker nevus, ipsilateral hypoplasia of the breast, and skeletal defects such as scoliosis. In the Proteus syndrome, the associated epidermal nevus is of a flat, velvety, nonorganoid type. The CHILD syndrome occurs almost exclusively in girls. The associated CHILD nevus shows unique features such as a diffuse form of lateralization, ptychotropism, and microscopic changes of verruciform xanthoma. The five epidermal nevus syndromes differ in their genetic basis. The Schimmelpenning and nevus comedonicus syndromes are most likely nonhereditary traits. By contrast, the pigmented hairy epidermal nevus syndrome and the Proteus syndrome may be explained by paradominant inheritance. The CHILD syndrome is caused by an X-linked dominant mutation exerting a lethal effect on male embryos. A correct diagnosis of these phenotypes is important for both recognition and treatment of associated anomalies as well as for genetic counseling.