l -dopa–induced dyskinesia (LID) is a common debilitating complication of dopamine replacement therapy in Parkinson's disease. Recent evidence suggests that LID may be linked causally to a hyperactivation of the Ras–ERK signaling cascade in the basal ganglia. We set out to determine whether specific targeting of Ras-guanine nucleotide-releasing factor 1 (Ras-GRF1), a brain-specific activator of the Ras–ERK pathway, may provide a therapy for LID. On the rodent abnormal involuntary movements scale, Ras-GRF1–deficient mice were significantly resistant to the development of dyskinesia during chronic l -dopa treatment. Furthermore, in a nonhuman primate model of LID, lentiviral vectors expressing dominant negative forms of Ras-GRF1 caused a dramatic reversion of dyskinesia severity leaving intact the therapeutic effect of l -dopa. These data reveal the central role of Ras-GRF1 in governing striatal adaptations to dopamine replacement therapy and validate a viable treatment for LID based on intracellular signaling modulation.