There is growing evidence implicating the subthalamic nucleus (STN) as a critical neural structure for the voluntary control of movement, especially in situations which require the stopping of movements. Evidence to date lacks the fine temporal scale to investigate the causal role of the STN in stopping. The present study takes a novel approach to manipulate STN functioning, using a short-train of disruptive deep brain stimulation time-locked to stopping events to observe its causal effects on stopping performance. Parkinson's disease patients with externalized bilateral STN electrodes performed a stop-signal task requiring a left or right arrow key press in response to a visual go-signal, but inhibit this response if a stop-signal was subsequently presented. Patients first performed a training block without stimulation to determine their stopping ability at a given stop-signal delay (SSD). Stimulation was then randomly delivered in the testing block during go-trials, and stop-trials with various SSD's (early, middle, late). We applied 250 ms of bilateral 130 Hz stimulation to the STN starting 50 ms after stop-signal onset (or theoretical onset during go-trials). Preliminary results reveal that stimulation has no effect on go-trial reaction time, but appears to have an effect on stopping performance depending on the SSD. Stimulation reduces the probability of stopping at the early SSD, but has no effect at the middle and late SSD. Though patient recruitment is ongoing, these initial findings provide novel human evidence for the causal role of the STN in stopping which will further inform current theories of behaviour control.