The aim of the study was to describe behavioural problems in children with cerebral palsy (CP) with and without epilepsy. The children were sampled from the Western Sweden CP register and were part of a European Union project. The Strength and Difficulties Questionnaire and questions on epilepsy were answered by one parent of each child. Medical records were reviewed. Parents of 83 children (44 males, 39 females) age range participated: 30 at Gross Motor Function Classification System levels I and II, and 53 at levels III to V; 60 had spastic age range 8 to 12 years (bilateral 42, unilateral 18) and 23 dyskinetic CP; 34 children had active epilepsy. The proportion of children with normal behaviour on the total difficulties score (TDS) of the Strength and Difficulties Questionnaire was significantly lower than normative data (57% vs 80%, p less than 0.001). Parents of 21 children (25%) considered their child's behaviour to be abnormal. Children with CP and epilepsy had a significantly higher median TDS (p = 0.03) than seizure-free children. In children with aided or no walking ability, the TDS was significantly higher in those with epilepsy (p = 0.04). Parents of 32 children (39%) considered their children's behaviour to have an impact on themselves and others. We conclude that behavioural problems are common in children with CP, and even more when epilepsy is present. Parents identify these problems, and professionals need to address them. (Contains 5 tables.)