Linear epidermal nevi are hamartomas that originate in embryonic ectoderm. For epidermal nevi associated with involvement of other systems, such as the skeleton or central nervous system, the term epidermal nevus syndrome has been introduced. Chromosomal aberrations have been suggested but not proven as an underlying cause. We performed cytogenetic studies of skin cells from two unrelated men who had a verruciform epidermal nevus. Variegated translocation mosaicism with an identical breakpoint localized at the long arm of chromosome 1 was present in both patients. Normal skin and blood lymphocytes showed normal karyotypes.