A 69-year-old woman with Parkinson's disease and levodopa-induced dyskinesias had a deep brain stimulation (DBS) electrode inserted into the right globus pallidus internus (GPi). During the operation, the GPi was mapped with dual microelectrode recordings. Stimulation through one microelectrode in GPi inhibited the firing of GPi neurons recorded with another microelectrode 600–1,000 μm distant. The inhibition could be obtained with pulse widths of 150 μs and intensities as low as 10 μA. Single stimuli inhibited GPi neurons for ∼50 ms. Trains of 300 Hz stimuli inhibited GPi neuron firing almost completely. Postoperatively, stimulation through macroelectrode contacts located in the posterior ventral pallidum controlled the patient's dyskinesias. The effect could be obtained with pulse widths of 50 μs and frequencies as low as 70–80 Hz. We postulate stimulation of the ventral pallidum controls dyskinesias by activating large axons which inhibit GPi neurons. © 2001 Movement Disorder Society.