Self-injurious behavior involving deliberate self-harm and suicide attempts by inmates while under custodial authority is a major problem for prisons and jails (prevalence, legal obligation for suicide prevention, and stress for officers). The differentiation of "serious" vs. "non-serious" and often manipulative suicide attempts as distinct phenomena, each with its own clinical features, is controversially discussed in current literature and a challenge for every diagnostician. If distinct clinical presentations and histories can be observed, an estimation of the seriousness of each act of self-injurious behavior can be simplified, whereby appropriate treatment of the individual case becomes possible. The aim of the study was to find differences between self-injurious behavior of "low seriousness" (i.e. low lethality and low suicidal intent) and of "high seriousness". Therefore, inmates showing self-injurious behavior were divided into subgroups of deliberate self-harm and suicide attempters on the basis of the act's intent and lethality. This was followed by a comparison of the clinical presentations of the individual inmates constituting the subgroups. Hence, 49 inmates showing self-injurious behavior were interviewed and tested with a variety of instruments (SCID-I and II, PCL-R, BDI-II, BHS, BSS, SIS, etc.), and their prison and health files were examined. The results indicate significant correlations between seriousness and some demographic, prison-related variables as well as different measures of depression. Negative, but nonsignificant correlations could be observed with regard to cluster B personality disorders. The PCL-R total score as well as PCL-R factor 1 showed a statistical trend for negative correlations with measures of seriousness. Inmates showing deliberate self-harm and suicide attempters seem to differ in a number of ways. Implications on how the individual prisoner should be treated are discussed.