In order to examine the importance of a range of potential risk factors for behaviour problems in children with severe intellectual disability, a sample was identified by the administration of a screening version of the Vineland Adaptive Behaviour Scales (VABS) to the parents of children aged 4-11 years attending six special needs schools in three adjacent inner London boroughs. Parents whose children had a VABS standard score of < or = 50 were interviewed using the Disability Assessment Schedule and both parents and teachers completed the Aberrant Behaviour Checklist. Most behaviour problems were more common in ambulant children, but problems less dependent on the ability to walk, such as sleeping difficulties, screaming and self-injury, were equally common in ambulant and non-ambulant children. Among ambulant children, there were few significant associations between the severity of the child's behaviour problems and the age or sex of the child, the presence or absence of epilepsy, and various indices of socio-economic disadvantage. Sleeping difficulties, overactivity, self-injury, destructive behaviour and autistic features, such as social withdrawal and stereotypies, were strongly associated with skills deficits, but aggression, temper tantrums and general disruptive behaviour were not. Limitations in daily living skills were better predictors of behaviour problems than were poor communication skills.