OBJECTIVE To explore longitudinal changes in brain activity in patients with Parkinson disease (PD), multiple system atrophy (MSA), and progressive supranuclear palsy (PSP) using task-based functional MRI (fMRI). METHODS A total of 112 individuals were scanned 1 year apart while performing a unimanual grip force task: 46 PD, 13 MSA, 19 PSP, and 34 healthy controls. The outcome measure was percent signal change in prespecified regions of interest: putamen, primary motor cortex (M1), supplementary motor area (SMA), and superior motor regions of the cerebellum (lobules V-VI). RESULTS Patients with PD showed a decline in functional activity over the course of 1 year in the putamen and M1 compared to controls. Changes after 1 year in MSA were exclusively extrastriatal, and included a reduction in functional activity in M1, SMA, and superior cerebellum. In PSP, all regions of interest were less active at 1 year compared to baseline. The functional activity of these regions did not change in the control group. CONCLUSIONS We provide evidence using task-based fMRI for cortical and striatal functional deterioration in PD over a 1-year period of time. Results also describe more widespread and unique patterns of functional changes in MSA and PSP compared to PD, suggesting distinct rates of disease progression in parkinsonian disorders that may assist in future clinical studies testing the potential efficacy of disease-modifying therapies.