Self-harming and suicide amongst adolescents are reported to be increasing in Europe and internationally. For young people in state care, this aspect of mental well-being is of particular concern. The aim of this study was to establish the incidence of suicidal ideation and behaviour amongst young people (age 16-21 years) leaving state care in one health and social care trust in Northern Ireland, and to explore the correlation between this and client risk factors that might inform professional practice. Data were gathered from 164 case files of the total 215 (response rate 76%) in relation to all open cases as of 30 April 2012 extracted by the relevant social workers through the use of a standard data collection tool. Twenty-seven per cent of young people known to the 16+ Teams engaged in self-harm or suicidal behaviour. There was a strong correlation between the number of self-harm incidents and the number of suicide attempts. The risk factors identified were consistent with the research base: "male", "unemployed", "alcohol and drug misuse", "adverse childhood experiences", "higher number of placement moves" "placement type" and "older age when entering care". Young people in more isolated placements seemed particularly at risk. The results of this study are of particular relevance to social workers and other professionals working with young people leaving state care.