Epidermal nevi, are mosaic disorders, caused by mutations during embryogenesis, hence affecting only those cells and tissues which had as a precursor this mutated cell. There are many types of epidermal nevi. Variable anomalies in other organs may be associated. In this paper we reviewed syndromic epidermal nevi, caused by mutations in HRAS, KRAS, NRAS or BRAF genes and found that the associations involving other organs than skin show a lot of overlap, however some differences are present, which depend more on the genetic background than on the type of nevus. Genetic testing may help to find a target for therapy in severe cases. (By Dr Marie-Anne Morren, https://jmg.bmj.com/content/early/2024/01/30/jmg-2023-109306 )