Institutions whose primary function is to provide diagnostic and long or short-term treatment services for children, adolescents, adults and/or older adults who have acute psychiatric disorders, require hospitalization for maximum benefit, and who may be a threat to themselves, to their families or to others if left in the community or placed in a less restrictive treatment setting. Services may include a comprehensive evaluation; 24-hour care in a supportive, therapeutic environment; counseling for the patient and family; adjunctive therapies, as needed; medication, if required; and an aftercare program following discharge. Psychiatric hospitals may also offer a range of outpatient mental health services.

Programs that provide guidance and support in resolving personal, social or psychological problems through an interactive process that encourages patients to make maximum use of their assets, strengthen effective existing defenses while eliminating those that are maladaptive, gain insight into conscious or unconscious conflicts, modify their goals and make other decisions that will help them improve their personal and interpersonal functioning and deal effectively with troubling situations in their lives.

Programs that are staffed by physicians who specialize in the prevention, diagnosis and treatment of mental, emotional and behavior disorders. Psychiatrists have specialized training, knowledge and skills which enable them to explore the biologic, psychological and social components of illnesses; and are licensed to prescribe medication, conduct physical examinations, order and interpret laboratory tests and EEGs and order brain imaging studies such as CT, CAT, MRI and PET scans as well as evaluate and treat psychological and interpersonal problems and provide continuing psychiatric care.