The majority of people who are homeless experience more health problems than the general population. However, in Ireland at least, there is a lack of specific information about the health of people who are homeless, in particular focussing on people at different stages of homelessness, including those at risk of homelessness. This snapshot study attempts to bridge this information gap and inform the development of effective homeless and health services for people who are homeless in Ireland. The study is based on information collected by the eight Simon Communities across Ireland. In total, 788 people using Simon projects and services participated in the study during one week in summer 2010. The questionnaire covered a wide range of issues, including physical and mental health, drug and alcohol use, complex needs, access to medical services, challenging behaviour and self-harm.