Health care for people with severe mental illness is often divided into physical health care and mental health care despite the importance of a holistic approach to caring for the whole person. Mental health nurses have an important role not only in preventing ill health, but also in promoting health, to improve the overall health among people with severe mental illness and to develop a more person-centred, integrated physical and mental health care. Thus, the aim of this study was to describe mental health nurses' experiences of facilitating aspects that promote physical health and support a healthy lifestyle for people with severe mental illness. Interviews were conducted with mental health nurses (n = 15), and a qualitative content analysis was used to capture the nurse's experiences. Analysis of the interviews generated three categories: (i) to have a health promotion focus in every encounter, (ii) to support with each person's unique prerequisites in mind and (iii) to take responsibility for health promotion in every level of the organization. The results show the importance of a health promotion focus that permeates the entire organization of mental health care. Shared responsibility for health and health promotion activities should exist at all levels: in the person-centred care in the relation with the patient, embedded in a joint vision within the working unit, and in decisions at management level.