Sleep problems are common in children with severe learning difficulties. Children with sleep problems are reported to have more behaviour problems, but daytime challenging behaviour has not been examined specifically. The current study was concerned with associations between sleep problems and challenging behaviour, as well as describing other clinical features of the childrens' sleep, as reported by parents. All children in the series showed some form of sleep disturbance, with settling problems, night waking and early waking in 44% of the sample. Children with sleep problems showed significantly more types of challenging behaviour and challenging behaviour of a greater severity than children without sleep problems, resulting in management difficulties for carers throughout the 24-h period. Reasons for this association and suggestions for intervention are discussed.