Children with Cerebral Palsy (CP) have difficulties walking at a normal or high speed. It is known that arm movements play an important role to achieve higher walking speeds in healthy subjects. However, the role played by arm movements while walking at different speeds has received no attention in children with CP. Therefore we investigated the use of arm movements at two walking speeds for children with diplegia (DI) and hemiplegia (HE) as compared to typically developing (TD) children. Arm and leg swing lengths were determined in 11 HE children and 15 DI children and compared to 24 TD children using 3D gait analysis at their preferred and "as fast as possible" walking speeds. We found that TD children increased walking speed more than both CP groups. HE children showed larger arm swings on the non-hemiplegic compared to the hemiplegic side for both walking speeds. In contrast to TD or DI children, the HE group did not show an increase in arm swing length with increasing walking speed. Their leg swing length was larger on the non-hemiplegic than on the hemiplegic side but only at the preferred walking speed. The DI children exhibited smaller leg swings at both walking speeds. Since arm swing is used both by DI (to increase speed) and by HE children (to compensate for the reduced movement on the affected side) it is argued that these movements are important and should be allowed (or even encouraged) in gait training procedures (such as treadmill training). Copyright © 2011 Elsevier Ltd. All rights reserved.