The genetic cause in women diagnosed with ovarian cancer (OC) under thirty years of age is unclear. It is known that the histology and genetics of these cancers are different to those in the general OC patient population. On reviewing the genes affected in women diagnosed under thirty years in the North-West of England we found genes involved in DNA mismatch repair, especially MSH2, to be affected. Genes important in overall OC risk such as BRCA1 and BRCA2 do not seem significant in this population. The risk of OC in women with an MSH2 mutation is >2% by age 35. (By Dr Niki Flaum, https://jmg.bmj.com/content/early/2023/03/08/jmg-2022-109055 )