© 2020 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd Objectives: To examine the relationship between step-rate and energy expenditure during treadmill walking in persons with PD and then further develop a step-rate cut-point for moderate-to-vigorous physical activity (MVPA) for persons with PD. Materials and Methods: The sample consisted of 30 persons with mild-to-moderate PD and 30 controls matched by age and sex. Participants performed a 6-minute bout of over-ground walking at comfortable speed, and then completed three, 6-minute bouts of treadmill walking at 13.4 m/min slower, comfortable, and 13.4 m/min faster than comfortable speeds. The three treadmill speeds were based on the initial over-ground walking speed. The total number of steps per treadmill walking bout was recorded using a hand-tally counter, and energy expenditure was measured using a portable, indirect spirometry system. Results: The results indicated a strong association between step-rate and energy expenditure for persons with PD (R2 =.92) and controls (R2 =.92). The analyses further indicated a steeper slope of the association for persons with PD compared with controls (t(58) = −1.87, P <.05), resulting in a lower step-rate threshold (t(58) = 2.19, P <.05) for persons with PD (~80 steps·per minutes) than controls (~93 steps·per minutes). Conclusion: Collectively, these results support the application of this disease-specific step-rate threshold for MVPA among persons with PD. This has important implications for physical activity promotion, prescription, and monitoring using accelerometers and pedometers for persons with PD to manage health and symptoms of PD.