Few analyses have been carried out in Japan concerning factors contributing to physical restraint of patients. We compared demographic data for 241 inpatients who were restrained during a 4-year period with data for 1093 inpatients who were not restrained in a general hospital psychiatric unit in Japan. Increased likelihood of restraint use was associated with older age, male gender, off-hours admission, involuntary hospitalization, transfer from other departments of the hospital, frequent hospitalization, absence of previous treatment, physical complications, history of suicide attempts, organic mental disorders, mental and behavioral disorders from psychoactive substance use, schizophrenia, schizotypal and delusional disorders. Importantly, physical complications not only were more prevalent among restrained than unrestrained patients, but additionally in restrained patients physical complications were associated with more prolonged hospitalization and periods under restraint than were associated with assaultive behavior or periods of unconsciousness. In conclusion, general hospital psychiatric units in Japan often treat patients with psychiatric disorders or symptoms that were associated with physical problems. Particular caution is needed in deciding whether such patients should be restrained since hospitalization may be prolonged or functional status compromised.