Mental Illness Defined Mental Illness Defined Mental Illness is a term used for a group of disorders causing severe disturbances in thinking, feeling and relating. They result in substantially diminished capacity for coping with the ordinary demands of life.
Mental illness can affect persons of any age, and they can occur in any family.
Several million people in this country suffer from serious long term mental illnesses. Mental illness is not the same as mental retardation. Those with a mental illness are usually of normal intelligence, although they may have difficulty performing at a normal level due to the illness. Schizophrenia affects approximately 1 person in 100. Symptoms include impairment of thinking, delusions and changes in behavior.