Non-suicidal self-injury (NSSI) is not uncommon in the general population, and is prevalent in association with a range of psychiatric disorders including major affective, personality and neuropsychiatric disorders. It often starts in childhood or early adolescence and involves repeated bouts of self-injurious acts, with similar risks among females and males. Such behaviours are distinguished from suicide attempts by an evident lack of lethal intent. Nevertheless, NSSI and suicidal behaviours occur frequently in the same persons, and NSSI can be a precursor of suicidal behaviour. NSSI typically seems to represent an effort to reduce overwhelming negative emotions, which can include dysphoric or depressive states. Indeed, the experience of immediate relief may contribute to the repetition of self-injurious behaviours. NSSI may also arise in response to a felt need for punishment or a desire to influence or seek help from others. NSSI behaviours occur far more frequently than suicide attempts, and usually are of low medical severity and rarely fatal. In addition to representing an important psychiatric syndrome in its own right, NSSI is a major risk factor for suicide that requires ongoing assessment of suicidal intent.