The aim of this study was to objectively assess the relationship between impaired forearm rotation and movement patterns of the upper arm and trunk in patients with hemiplegic cerebral palsy. For this purpose, 'extrinsic forearm rotation' was introduced as a parameter to quantify the cumulative result of all movements that supplement forearm rotation. The results of three-dimensional video analysis of the upper extremity and trunk in different reaching tasks in eight male and two female patients (mean age, 16 years and 2 months) were compared to those of 10 case-matched controls. The active forearm rotation impairment in the patient group as compared to the controls was combined with a significantly higher value for 'extrinsic forearm rotation'. In this way, we objectively measured compensatory movement patterns associated with impaired forearm rotation and, consequently, we advocate assessment of the overall movement strategy rather than just the forearm deformity in patients with hemiplegic cerebral palsy. © 2006 Elsevier B.V. All rights reserved.