["Toddlers learning to walk adopt specific 'guard' arm postures to maintain their balance during forward progression. In Cerebral Palsy (CP), the cause of the altered arm postures during walking has not been studied.", 'To investigate whether the altered arm posture in children with CP is a compensation for instability during walking.', 'Vertical and horizontal hand position, and upper arm elevation angle in the sagittal plane were determined in eleven children with unilateral CP, fifteen children with bilateral CP using 3D gait analysis and compared to twenty-four TD children. A correlation analysis of these measures of arm posture to step width was made to examine the relationship between arm posture and instability.', 'The hand position of children with CP was more elevated and anterior, and their upper arm was rotated more posterior than TD children. Children with unilateral CP held their most affected hand higher than their least affected. Increasing the speed accentuated the differences between groups for hand elevation. Step width correlated positively with horizontal hand position of the least affected arm in children with CP.'] Is altered arm posture in children with cerebral palsy related to instability during walking?