Genomic testing for people affected by rare diseases will occasionally identify a gene variant or other finding that is not related to the reason for testing. This guidance on managing such “incidental findings” has been developed to support the specialist genomics workforce within the national health services in the UK and Ireland. It describes the principles of reporting incidental gene variants if there is a high likelihood of developing the disease and available treatment likely to improve the outcome. Our overarching objective is to facilitate greater consistency in the reporting of incidental findings to patients and their families. (https://jmg.bmj.com/content/early/2026/08/06/jmg-2026-111522)