Hemiplegic cerebral palsy (HCP) patients have transverse-plane gait deviations that may include the "uninvolved" side. The aim of this study is to quantify the static rotational profile, the dynamic position during gait and determine whether any correlations between the involved and uninvolved side exist. A total of 171 subjects that met the inclusion criteria of HCP and no prior history of bony surgery were reviewed. Clinical and gait measurements were analyzed and compared between subjects and a population of typically developing (TD) children. Among children with HCP, static internal hip rotation of the affected limb was strongly correlated to static internal hip rotation on the unaffected limb (r=0.543, P<0.0001).There were 100 patients with maximum static internal rotation ≥66% of the total arc of motion in the affected hip. These subjects showed significant differences of static range of motion measures of the affected hip compared with TD. They also showed statistical significant differences between the dynamic measures of the affected limb of HCP and TD for mean pelvic rotation, mean hip rotation, and mean knee progression.In these 100 subjects, 23 patients had a maximum static internal rotation ≥66% of the total arc of motion on the unaffected hip and there were 77 subjects with <66% static internal rotation. Pelvic rotation and hip rotation were statistically different between these 2 groups, but knee progression angle was not significant. The "unaffected" side in patients with HCP influence gait kinematics. If static internal hip rotation exceeds 66% of the total arc of motion, almost all studied static and gait parameters were abnormal in HCP children, regardless if it was the affected side. Compensations on the "unaffected" side seem to be somewhat limited if the anatomic alignment is significantly asymmetric. This may be 1 reason pelvic transverse-plane changes after femoral rotation osteotomy are unpredictable. Level II.