The present study examines 89 separate incidents of self-injurious behaviour displayed by 60 male young offenders, incidents which were recorded by prison staff on "self-harm" forms. The results show that the reasons for raising a self-harm form can be separated into two main categories: actual self-injury by the inmate or behaviours believed by staff to indicate a risk of self-injury. A believed risk of self-injury as opposed to actual self-injury was the most frequently reported reason for opening a self-harm form, with verbal threats of self-injury being the most frequently reported type of behaviour. Self-injury does appear to occur relatively early on in periods of custody and inmates who display self-injurious behaviour appear distinct from the rest of the prisoner population in a number of ways. Differences are also evident between those with only one form raised on them and those with more than one form raised. Directions for future research are discussed.