Background: Self-injury is defined as the intentional injuring of one's own body without apparent suicidal intent. Self-harm is encountered frequently in psychiatric hospitals. Deliberate self-harm may be found in patients with a variety of diagnoses, including substance abuse, major depression, schizophrenia and especially borderline personality disorder. Objectives: This study aimed to investigate the prevalence of self-injury and possible relating factors in patients with psychiatric diseases. Patients and Methods:In this cross-sectional study, 42 patients with self-injury referred to Lavasani hospital in Tehran, Iran, were selected by random sampling during 2013 -2014. The prevalence of self-injury, site and tools of self-injury and also possible contributing factors were evaluated. T-test and Fisher's exact test were used to analyze data. Results: Mean distribution of self-injury in patients was 12.5%. Sharp object was the tool of injury in 90.5% of the patients, 4.8% by fire, 2.4% by stone and 2.4% by other attempted to self-injury. In 76.2% of the patients extremities were the site of injury. In 19%, 2.4% and 2.4% head and neck, trunk and abdomen were the sites of injury, respectively. There was a significant association between type of disorder and tool and body site of self-injury (P < 0.001). Conclusions: It can be concluded that schizophrenia and drug-induced psychotic disorder were the most common types of disorders that are at risk of self-injury.