Objective: To evaluate the occurrence and severity of FOG in provoking situations during a standard videorecorded walking task. To use this method to compare the effects of STN-DBS and L-dopa.To look for the predictive value of the test. Background: Specic situations provoke freezing of gait (FOG) in Parkinson’s disease (PD). The sensitivity of these situations to detect FOG and the relative response of FOG to L-dopa and subthalamic nucleus deep brain stimulation (STN-DBS) is unknown. Method: The video recordings of a structured patient assessment before and 10 months after DBSimplantation of 124 patients with PD and FOG according to the Unied rating scale, item 14, were analyzed blinded in six different conditions: before electrode implantation off- and on-L-dopa (OFF/ON-drug) and after surgery off- and on-stimulation (OFF/ON-stim) and L-Dopa. FOG was quantied by rating four different FOG subtypes (start, turning, reaching a destination and open space hesitations) according to severity (no freezing, shufing forward with small steps, trembling in place or complete akinesia). Cumulative link mixed models were calculated to investigate the effect of medication and stimulation. The predictive value of baseline assessment for the freezing outcome was determined. Results: Eighty-one percent of patients presented at least one FOG subtype. Both interventions improve all FOG subtypes similarly. The effect size of L-dopa and STN-DBS on subtypes were similar (p>0.05), and the combined intervention had a stronger effect on FOG severity (p<0.0001) compared to each response separately. FOG severity was lower at follow-up off compared to baseline off condition (p<0.02) demonstrating a carry-over effect of STN-DBS. The positive predictive value (PPT) was 91% and the negative predictive value (NPV) was 44%. Conclusion: Turning hesitation is the most sensitive provoking situation. STN-DBS has the same effect size on FOG as L-Dopa; the combined intervention has a stronger impact. The scaling of freezing has a good PPT but the NPP is only poor. To cite this abstract in AMA style: O. Gavriliuc, S. Paschen, A. Andrusca, C. Schlenstedt, G. Deuschl. Clinical patterns of gait freezing in Parkinson’s disease and their response to interventions: an observer-blinded study [abstract]. Mov Disord. 2019; 34 (suppl 2). https://www.mdsabstracts.org/abstract/clinical-patterns-of-gait-freezing-inparkinsons-disease-and-their-response-to-interventions-an-observer-blinded-study/. Accessed December 4, 2023. MDS Abstracts - https://www.mdsabstracts.org/abstract/clinical-patterns-of-gait-freezing-in-parkinsonsdisease-and-their-response-to-interventions-an-observer-blinded-study/