OBJECTIVE: We studied the effects of subthalamic nucleus (STN) stimulation vs levodopa on freezing of gait (FOG) and gait impairments in a large consecutive series of patients with Parkinson disease with bilateral STN stimulation. METHODS: One hundred twenty-three patients performed the Stand Walk Sit Test before and 1 year after surgery both off and on levodopa and off and on stimulation. RESULTS: Before surgery, 25 patients displayed FOG episodes and 48 were unable to complete the Stand Walk Sit Test when off levodopa. Both symptoms were alleviated by levodopa. After surgery, STN stimulation reproduced the improvement induced by levodopa before surgery in all but two patients with FOG and five others unable to walk. In 11 patients, FOG or inability to perform the test first occurred after surgery. In all patients but those experiencing FOG during the Stand Walk Sit Test before surgery, the benefit of STN stimulation did not reach that of levodopa before surgery. In patients with FOG before surgery, the effect of STN stimulation did not differ from that of levodopa either before or after surgery. CONCLUSIONS: Overall, subthalamic nucleus stimulation improved levodopa-responsive freezing of gait in most patients, although it was not always as effective as levodopa to improve gait impairments. In addition, surgery can induce gait problems in some patients.