OBJECTIVE: Forced use, or constraint-induced, movement therapy has shown some efficacy in the rehabilitation of adults with chronic hemiparesis as a result of stroke. We used restraint of the unimpaired arm to ascertain whether this would improve function of the paretic arm in children with chronic (>1 year) hemiparesis. METHODS: Twelve hemiparetic treatment children (age 1-8 years) received a plaster cast on the unimpaired arm for 1 month; 13 hemiparetic control children did not. Peabody Developmental Motor Scales (PDMS) were performed on all treatment and control children immediately before and after casting and again 6 months later when controls crossed over to receive casts. Thus, PDMS were performed at entry, then 1 month, 6 months, and 7 months after entry. Any noted change in functional ability was also elicited by parental report. The frequency of visits to physical and occupational therapy was recorded. RESULTS: The 12 treatment (casted) children improved 12.6 PDMS points after 1 month of casting; the 13 control children improved 2.5 points. Improved PDMS scores persisted 6 months later when 7 treatment children returned. Similar results were obtained in the crossover when 10 control children received casts. Parental report corroborated improvement in casted children (22 of 22 parents) and its persistence at follow-up (21 of 22 parents). Receiving ongoing physical/occupational therapy did not seem to account for these results: control children received more (2.1 visits/wk) than treatment children (1.4 visits/wk). CONCLUSIONS: Forced use can be an effective rehabilitation technique in children with chronic hemiparesis.