A major barrier to research on Parkinsons disease (PD) is inaccessibility of diseased tissue for study. One solution is to derive induced pluripotent stem cells (iPSCs) from patients with PD and differentiate them into neurons affected by disease. We created an iPSC model of PD caused by triplication of SNCA encoding -synuclein. -Synuclein dysfunction is common to all forms of PD, and SNCA triplication leads to fully penetrant familial PD with accelerated pathogenesis. After differentiation of iPSCs into neurons enriched for midbrain dopaminergic subtypes, those from the patient contain double -synuclein protein compared to those from an unaffected relative, precisely recapitulating the cause of PD in these individuals. A measurable biomarker makes this model ideal for drug screening for compounds that reduce levels of -synuclein, and for mechanistic experiments to study PD pathogenesis.