In all 21 children with spastic cerebral palsy (CP) underwent surgery involving selective posterior rhizotomy (SPR), followed by six months intensive physiotherapy (PT). Neurological and physiotherapeutic assessments were made one, three and five years after the operation. The children undergoing surgery were compared to 21 comparison children who took part in a regular physiotherapy programme during the same time period. At the preoperative assessment, the children undergoing surgery were similar to the comparative children in terms of age, sex, type of CP, spasticity of the legs and mean functional scores. The children were selected for SPR on the basis of more than half a year's arrest of motor development, which was the only significant difference to the comparative group. Motor function was measured using two different methods, the Illinois-St Louis Scale and the Gross Motor Functional Classification System (GMFC). Both groups experienced steady development during the five-year follow-up period and no significant differences were observed in the mean functional scores between the groups. We conclude that this comparative study, like most controlled studies, failed to demonstrate any additional effect of SPR on motor development of children with spastic CP. Nevertheless, SPR may contribute to a resumption of motor development in children with arrested motor development despite vigorous conservative therapy. SPR is therefore justified as treatment in selected cases.