Stimulation of the subthalamic nucleus (STN) is an effective treatment for advanced Parkinson's disease (PD), but the medication requirements after implant are poorly known. We performed a long-term prospective evaluation of 20 patients maintained at stable dopaminergic therapy for 5 years after bilateral STN implants, who were evaluated 6 months, 1 year, 3 years, and 5 years after surgery. We measured, during the entire observation period, the effect of deep brain stimulation on motor and functional outcome measures, the levodopa equivalent daily dose and the total electrical energy delivered. At 5 years, the UPDRS motor score had improved by 54.2% and levodopa equivalent dose was reduced by 61.9%, compared with preimplant. Dopaminergic medication remained stable during the observation period, but energy was progressively increased over time. Rest tremor, rigidity, gait, lower and upper limb akinesia, and total axial score were improved in decreasing order. Postural stability and speech improved transiently, whereas on-period freezing of gait, motor fluctuations and dyskinesias recovered durably. Functional measures did not show improvement in autonomy and daily living activities after STN implant. Chronic STN stimulation allows to replace for dopaminergic medications in the long-term at the expense of an increase of the total energy delivered. This is associated with marked improvement of motor features without a matching benefit in functional measures.