It is with great sorrow that I report that our dear friend and colleague Professor Dermot O’Reilly died suddenly after a very short illness on Monday 30th October 2023. Instrumental to the foundation of the Northern Ireland Longitudinal Study (NILS) and the Northern Ireland Mortality Study (NIMS) in the early 2000’s, Dermot also acted as the first Director of the NILS Research Support Unit from 2006. As he continued to lead in the development of the Northern Ireland data and research infrastructure, he moved on to become Director of the Administrative Data Research Centre Northern Ireland (ADRC NI) from 2007 until the present day. A continued friend of the NILS/NIMS and administrative data research, he made a massive impact on the research community mentoring and encouraging a wealth of researchers including Dr Aideen Maguire, Dr Mark McCann, Dr David Wright, Dr Karen Galway, Dr John Moriarty as well as close collaborators like Dr Michael Rosato…to name a few. Dermot will be missed by all those with whom he came in contact during his professional life but it is amongst close friends and family that his loss will be most keenly felt and so it is to them that we also pass our condolences and regrets, and the comfort that he made a big positive difference to the lives he touched during his career.