A survey was conducted involving 664 individuals admitted to a public psychiatric hospital in Tokyo Prefecture between July 15,2004 and July 14,2007 as a result of involuntary admission by order of the prefectural governor（hereafter, involuntarily admitted patients）. The characteristics of patients with a focus on the effects of the Medical Treatment and Supervision Act were investigated in 656 patients,excluding eight patients for whom information at the time of involuntary admission was unclear. The proportion of patients in the present survey who had been reported by prosecutors was markedly low compared to nationwide and previous surveys. This was thought to be a result of the fact that the proportion of patients reported by the police,which tend to include emergency cases, was high due to the characteristics of the present hospital as well as the regional characteristics of Tokyo Prefecture. The characteristics of involuntarily admitted patients tended to be similar to those observed in previous surveys on involuntarily admitted patients at the present and other hospitals in Tokyo Prefecture. Comparison of the characteristics of involuntarily admitted patients and problem behaviors that instigated admission before and after implementation of the Medical Treatment and Supervision Act showed no clear differences,indicating that the act had no marked effect on involuntary admission by order of the prefectural governor. In addition, only a small proportion of patients with problem behaviors corresponding to actions described in the Medical Treatment and Supervision Act were reported by prosecutors, suggesting that such patients were mostly reported by the police. In cases where patients faced involuntary admission by order of the prefectural governor after being reported by the police, the prosecutor may have either been unaware of the patient or,if aware,had not filed a petition. Issues may include clues for investigation in addition to the roles of judicial police officers and prosecutors in investigation procedures in the former case,and the discretion of prosecutors in the latter case. While opinions on the appropriateness of actively applying the Medical Treatment and Supervision Act to these patients vary depending on the interpretation of the act's legal characteristics,it appeared that involuntary admission by order of the prefectural governor was at present not clearly distinguished from the Medical Treatment and Supervision Act. Involuntary admission by order of the prefectural governor and the Medical Treatment and Supervision Act are systems that have significant implications for patients with mental disorders, who are likely to cause injury to themselves or others. In order to facilitate the provision of appropriate medical care, it is important to clarify the systematic relationships within the legal system.