Background Patients with Parkinson's disease (PD) may develop freezing of gait (FOG) with chronic deep brain stimulation (DBS) of the subthalamic nucleus (STN) at the commonly used frequency of 130 Hz and FOG can be ameliorated by 60 Hz stimulation in some patients. It is not clear whether the development of FOG is due to the disease progression or the chronic stimulation at this 130 Hz frequency.

Aims To investigate the effect of stimulation frequency on immediate FOG in newly activated STN DBS patient with PD and determine if stimulation frequency alone could affect the FOG.

Methods Two cases of PD who developed FOG immediately upon activation of the newly placed STN DBS were studied for the effect of stimulation frequency on FOG in both `off' and `on' medication status.

Results Both patients developed severe FOG with the commonly used 130 Hz stimulation. Switching the frequency to 60 Hz immediately alleviated the FOG, without change in contacts, voltages and pulse widths. This frequency effect on FOG was present in both `off' and `on' statuses and remained effective during the 10-month follow-up period.

Conclusion These two cases demonstrate that lower frequency stimulation of 60 Hz could improve FOG, while the commonly used 130 Hz stimulation could cause FOG or make it worse. In addition, the beneficial effect of low frequency DBS was additive to dopaminergic medication effect and included other axial symptoms.