Over half of patients with PD eventually develop freezing of gait (FoG), an intermittent failure to initiate or maintain walking that is often associated with trembling of the legs. We tested 21 PD with FoG, 27 PD without FoG, and 21 healthy elderly people in a clinic with the Intrumented Timed Up and Go test (ITUG). FoG was quantified from the power spectral density of the antero-posterior shank acceleration from which a Frequency Ratio was calculated as the square of the total power in the 3-8 Hz band, divided by the square of the total power in the.5-3 Hz band. Spatiotemporal gait parameters calculated from synchronized gyroscopes on the two legs were also measured in these subjects. The Frequency Ratio was significantly larger in freezers than in non-freezers or control subjects. It better differentiated gait disorders between PD subjects with and without FoG than traditional gait measures such as stride length, stride velocity and double support time. The Frequency Ratio was validated as significantly correlated with self-perceived severity of gait and balance confidence. This Freezing Ratio will be useful to quantify FoG during a simple ITUG, a popular clinical test of mobility.