Mental Retardation, disorder in which a personís overall intellectual functioning is well below average, with an intelligence quotient (IQ) around 70 or less. Individuals with mental retardation also have a significantly impaired ability to cope with common life demands and lack some daily living skills expected of people in their age group and culture. The impairment may interfere with learning, communication, self-care, independent living, social interaction, play, work, and safety. Mental retardation appears in childhood, before age 18.
About 1 percent of the general population has mental retardation, although some estimates range as high as 3 percent. Mental retardation is slightly more common in males than in females. It occurs in people of all racial, ethnic, education, and economic backgrounds.