In general, a distinct unit of a hospital that provides acute or long-term care to emotionally disturbed patients, including patients admitted for diagnosis and those admitted for treatment of psychiatric problems on the basis of physicians' orders and approved nursing care plans. Long-term care may include intensive supervision to the chronically mentally ill, mentally disordered or other mentally incompetent persons; (2) For Medicare, a distinct part of a general acute care hospital admitting only patients whose admission to the unit is required for active treatment, whose treatment is of an intensity that can be provided only in an inpatient hospital setting, and whose condition is described by a psychiatric principal diagnosis contained in the Third Edition of the American Psychiatric Association Diagnostic and Statistical Manual or in Chapter 5 (Mental Disorders) of the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). The unit must furnish, through the use of qualified personnel, psychological services, social work services, psychiatric nursing, occupational therapy, and recreational therapy. The unit must maintain medical records that permit determination of the degree and intensity of treatment provided to individuals who are furnished services in the unit; the unit must meet special staff requirements in that the unit must have adequate numbers of qualified professional and supportive staff to evaluate inpatients, formulate written, individualized, comprehensive treatment plans, provide active treatment measures and engage in discharge planning.