Objective To develop a reliable, objective and sensitive measure of axial trunk rotations in PD, which can be applied in an ambulatory setting. Methods To quantify turning motion, two angular velocity transducers attached to the lower back measured angular velocity of the trunk in the yaw plane (i.e., around the longitudinal axis) and the roll plane (i.e., medio-lateral movements) in freely moving subjects who were instructed to walk and make various types of turning movements. Results Turn duration was longer in PD patients compared to controls. Peak yaw and peak roll angular velocities were lower in PD patients compared to controls during all turning tasks. Conclusions This new approach to measure trunk sway during a simple turning task might serve as an instrument to objectively quantify turning while walking in PD. Significance It proves difficult to objectively assess turning performance based upon history taking or clinical examination alone. Objective and easy measurement of axial turning in PD might be used for clinical evaluation, but also in a domestic setting as outcome measure in intervention studies. Further research should focus on the clinical relevance of the new quantitative approach described in this paper, e.g., to detect freezing of gait episodes.