Liaison mental health nursing is an evolving specialist area of mental health nursing in the United Kingdom (UK). It has many similarities with ‘psychiatric consultation liaison nursing’ practiced in the United States of America (USA), but there have been differences in its development. It is well established in general health settings where psychological problems are most apparent, such as accident and emergency services and oncology. However, it lacks clear developed, and how it is currently described. The position of liaison mental health practice within nursing is discussed, and also its relationship to liaison psychiatry. The theoretical base of this specialty may be seen as an integration of biological, psychological and sociological perspectives. There is no current programme of training for liaison mental health nurses, and this is likely to inhibit its recognition as a specialty in the UK. As interest grows in psychosocial aspects of physical health, liaison mental health nursing has the potential to provide a focus for research within nursing. Areas for further development are reviewed, and a research agenda is proposed.