The prevalence of Parkinson disease (PD) is growing fast, amplifying the quest for disease-modifying therapies in early disease phases where pathology is still limited. Lifestyle interventions offer a promising avenue for preventing progression from prodromal to manifest PD. We illustrate this primarily for 1 specific lifestyle intervention, namely aerobic exercise because the case for the other main lifestyle factor (dietary interventions) to modify the course of prodromal PD is currently less persuasive. Various observations have hinted at the disease-modifying potential of exercise. First, studies in rodents with experimental parkinsonism showed that exercise elicits adaptive neuroplasticity in basal ganglia circuitries. Second, exercise is associated with a reduced risk of developing PD, suggesting a disease-modifying potential. Third, 2 large trials in persons with manifest PD indicate that exercise can help to stabilize motor parkinsonism, although this could also reflect a symptomatic effect. In addition, exercise seems to be a feasible intervention, given its minimal risk of side effects. Theoretical risks include an increase in fall incidents and cardiovascular complications, but these concerns seem to be acceptably low. Innovative approaches using gamification elements indicate that adequate long-term compliance with regular exercise programs can be achieved, although more work remains necessary to demonstrate enduring adherence for multiple years. Advances in digital technology can be used to deliver the exercise intervention in the participant's own living environment and also to measure the outcomes remotely, which will help to further boost long-term compliance. When delivering exercise to prodromal participants, outcome measures should focus not just on phenoconversion to manifest PD (which may well take many years to occur) but also on measurable intermediate outcomes, such as physical fitness or prodromal nonmotor symptoms. Taken together, there seems to be sufficient evidence to advocate the first judicious attempt of investigating exercise as a disease-modifying treatment in prodromal PD.