Among the many clinical skills that psychiatrists must acquire, the ability to assess the risk of patients killing themselves is probably the most important and demanding. It is often a crucial factor when making clinical decisions, such as in the choice of treatments, when deciding whether admission to a psychiatric hospital is necessary and when implementing the Mental Health Act. This review first explores the problems in assessing suicide risk. Subsequently, the risks of suicide for patients with major psychiatric disorders and for particular clinical populations, including hospitalised patients and suicide attempters, are examined together with the findings from research investigations which can assist psychiatrists when making decisions about the risk of suicide.