Personality traits, family environment and maltreatment episodes are often associated with nonsuicidal self-injury (NSSI); however, research on these associations has shown mixed results. The aim of the present study was to clarify the effects of these factors on the presence and the severity of NSSI among a sample of Italian students who attended secondary schools (N = 267, mean age = 17.03 SD = 0.866). The results showed that personality traits, family environment and maltreatment differently predicted the presence and the severity of NSSI. Self-injurers were more impulsive and aggressive than non-self-injurers and reported poorer relationship quality with their mothers and more sexual and physical abuse episodes than non-self-injurers. Conversely, the frequency of NSSI behaviours was predicted by the presence of less impulsiveness, more anxiety and aggressiveness, poorer relationship quality with both parents and a lower degree of identification with the father. Finally, more frequent self-injurers also reported more sexual abuses and neglect episodes than less frequent self-injurers.