A total population study was undertaken in two areas of England to identify the situation and characteristics of people reported to exhibit challenging behaviors. We found that: (1) challenging behaviors are shown by 10–15% of people with mental retardation who are in contact with educational, health or social care services for people with mental retardation; (2) the most common forms of challenging behaviors reported were ‘other’ behavior (shown by 9%–12% of all people screened), aggression (7%), destructive behavior (4%–5%) and self-injury (4%); (3) the majority of people identified showed two or more of these four general forms of challenging behavior; (4) approximately two-thirds of the people identified were boys/men; (5) close to two-thirds of the people identified were adolescents or young adults; (6) approximately 50% of the people identified as showing more demanding challenging behavior were living with their families; (7) people who showed more demanding challenging behavior were more likely to need greater levels of assistance in eating, dressing and washing, be incontinent and have more restricted expressive and receptive communication.