Objective: Self-harm and attempted suicide are risk factors for suicide in psychiatric hospital in-patients. This study aimed to analyse the circumstances of self-harm and suicide attempts in a Japanese psychiatric hospital so as to improve management and care. Methods: Incident reports of self-harm and suicide attempts during a 12.4-year period from November 2000 to March 2013 were reviewed. A descriptive analysis was conducted in terms of age, sex, and diagnosis of patients, as well as level, ward, situations, and causes of incidents. Results: During the study period, 90 cases of self-harm and attempted suicide involving 58 patients were reported. The rate of self-harm and suicide attempts was 0.05 per 1000 patient-days. The types of self harm and suicide attempts included hanging (n = 25), wrist cutting (n = 19), ingestion of foreign objects (n = 17), and others (n = 29). The single case of completed suicide involved hanging, in a patient with schizophrenia. Among 55 patients with relevant data, the most common clinical diagnosis was mood disorder (41.8%), followed by schizophrenia (36.4%). Mood disorder was 3.5 times as prevalent in females as in males (14 vs. 4). Fourteen patients with mood disorder (n = 8) or schizophrenia (n = 6) were repeatedly involved in 46 of 89 cases of self-harm or attempted suicide; 11 were female. One woman with mood disorder attempted suicide 9 times within the same year. The top 3 management and care factors related to self-harm and suicide attempts were failure to adhere to preventive procedures (28%), insufficient therapeutic communication (28%), and difficulty in predicting suicide (20%). Conclusion: Self-harm and suicide attempts at this psychiatric hospital occurred at a rate of 0.05 per 1000 patient-days between late 2000 and early 2013. Efforts are needed to increase compliance with suicide prevention procedures and therapeutic communication, so as to improve management and care of psychiatric in-patients and prevent them from committing suicide.