The Mental Health Promotion and Welfare Act, revised in 2016, tightened the involuntary admission regulations and processes, such as reporting involuntary admission within 3 days of admission, secondary diagnosis within 2 weeks, and admission suitability evaluation within 1 month, to improve the human rights of the mentally handicapped. The Admission Management Information System (AMIS) was also developed in 2017 to support these procedures and manage patients who were involuntarily admitted to the hospital.We analyzed 34,685 cases of involuntary admission registered in the AMIS between July 2017 and June 2018. The general characteristics, diagnosis, admission hospital, admission type, age, and admission duration were examined, and diagnoses and the length of stay per hospital were analyzed.Among the research subjects, 62.8% were male and 37.2% were female. A total of 70.8% had medical insurance and 28.5% had medical aid. A total of 67.8% of patients received secondary diagnosis by a psychiatrist who worked for a public or designated institution, 24.6% received secondary diagnosis by a psychiatrist who worked for the same institution as the primary psychiatrist, and 8.4% received primary diagnosis by a psychiatrist who admitted the patient. For diagnosis, F2 code was the most common at 38.1%, followed by F1 code at 29.1% and F3 code at 17.9%. For cases with only a primary diagnosis, F1 code diagnosis was the most common at 37.6%. For types of hospitalization, and admission by legal guardians was the most common at 93.2%, while administrative admission was at 6.7% and admission by legal guardians to a long-term care facility was at 0.1%. The average length of hospitalization duration was 74.4 days. A stay between 31 and 90 days was the most common (39.3%), and hospital stay of <14 days was at 16.6%. The number of involuntary admissions for every 100,000 people was 67 cases on average, and this number was the highest in the South Gyeongsang Province, at 105.8 cases. Length of stay by diagnosis was the longest for F7 code (118 days), followed by F1code (91 days). Patients older than 60 years constituted 31.7% of the total sample, and those younger than 20 years showed the highest proportion in patients with diagnoses from F4 to F9 code.Analyzing the involuntary admissions registered on the AMIS for 1 year revealed various information, such as the type of admission, sex, age, diagnosis, region, and admitted hospital. These results could be used to improve involuntary admission policies and mental health systems.