We previously reported clinical improvement, increase in putamen [(18)F]-dopa uptake on PET imaging, and neuropathologic evidence of sprouting of dopaminergic fibers following chronic intraputaminal delivery of glial cell line-derived neurotrophic factor (GDNF) in idiopathic Parkinson disease (PD).(1-3) We now provide clinical and PET evidence of persistent efficacy lasting for at least 3 years following cessation of GDNF infusion in a patient with PD. This is a single-case observational study, providing Class IV evidence.