BACKGROUND AND PURPOSE: It has been proposed that a structured exercise program will increase overall physical activity in people with Parkinson's disease (PwPD). Initial studies present conflicting results. The aim of this project was to determine the impact of a home-based aerobic exercise (AE) program on overall physical activity over 12 months in PwPD. METHODS: This project was a secondary analysis of data gathered during a multisite randomized controlled clinical trial. Individuals with Parkinson's disease were randomized to a home-based AE or usual and customary care (UCC) group. The AE group exercised 3×/wk, progressing to 30-45 minutes, for 12 months on a commercially available stationary cycle. Physical activity for both groups was captured by a lower extremity activity monitor. The difference in overall physical activity between the UCC and AE groups was evaluated using a linear mixed model. RESULTS: A total of 118 and 119 people were included in the AE (mean [standard deviation] age 62.5 [8.1] years; 67.8% male) and UCC (mean [standard deviation] age 65.3 [8.2] years; 66.4% male) groups, respectively. Mean physical activity per day was 19% (~1000 steps) higher in the AE group compared with the UCC group. In the AE group, physical activity was 85% higher on exercise than nonexercise days. Both groups exhibited an overall negative trend in physical activity over 12 months. CONCLUSIONS: Physical activity gained from AE in a cohort of PwPD was additive to usual activity, as physical activity in the AE group remained considerably higher than the UCC group throughout the year. The increase did not arrest the gradual annual declines in physical activity among PwPD but may create a buffer to the decline. Physical therapists should prescribe structured AE programs to increase overall physical activity in PwPD.