Objective: To test the hypothesis that balance control in Parkinson’s disease (PD) is asymmetrically affected using system identification techniques. Background: PD is an asymmetrical disease. It is unknown whether axial symptoms, such as impaired balance, also show asymmetry. Clinical scales used to assess disease severity do not explicitly evaluate asymmetries in axial symptoms. Evaluation of asymmetrical balance control might improve our understanding and treatment of axial symptoms. Methods: Eight patients with idiopathic PD were asked to maintain their balance during continuous random translational platform movements. Body sway angle and reactive forces of each foot were recorded. These yielded the Frequency Response Function (FRF) of the stabilizing mechanisms, which expresses the amount and timing of the generated corrective torque in response to sway at the specified frequencies. The FRFs were used to calculate the relative contribution of each ankle to the total amount of generated corrective torque to resist the perturbations. In addition, the amount of weight bearing of each leg was calculated. Furthermore, the motor part of the UPDRS and the Hoehn & Yahr disease stage were also evaluated. Results: Results showed that six out of eight patients responded asymmetrically to the induced platform perturbations as shown by corrective ankle torques. Hence, one leg contributed significantly more to balance control than the other and there was no clear relationship between the contribution to weight bearing and to balance control. Conclusions: Balance control in PD patients proved asymmetrical for some patients. This asymmetry of axial symptoms can be reliably identified with system identification techniques in the frequency domain. In this way, the effects of different treatments can be identified for each leg separately.