Out of the 73 patients with spastic cerebral paresis in a paediatric department in one of the Centres for the Care of the Mentally Retarded, 23% had dislocation of the hip and 18% subluxation. Among the most severely affected patients with tetraplegia and profound mental retardation, a total of 67% had dislocation or subluxation. None of the patients with dislocation of the hip were able to walk, with or without support. As dislocation in cerebral paresis frequently results in scoliosis, poor sitting position, a prolonged period with pain and makes nursing care difficult, it is possible that the intellectual development is influenced simultaneously with the impaired motor development. This complication can only be avoided if it is recognized in time by radiographic investigation of the hips.