PURPOSE: To explore reliability and inherent variability of physical activity (PA) and exercise self-efficacy (ESE) questionnaires and association of PA with ESE in people with Parkinson disease (PwP). MATERIAL AND METHODS: International Physical Activity Questionnaire (IPAQ), Brunel Lifestyle Physical Activity Questionnaire (BLPAQ), and ESE data were collected from 30 PwP (NCT049222190). Intraclass correlation coefficients (ICC) and Minimal Detectable Change (MDC RESULTS: Test-retest reliability was moderate for IPAQ, good for BLPAQ Planned, moderate for BLPAQ Unplanned, and moderate for ESE. Test-retest reliability was good for IPAQ ≤ 2000 MET-minutes/week and poor for IPAQ ≥ 2000 MET-minutes/week as per subgroup analysis. MDC CONCLUSION: IPAQ, BLPAQ, and ESE exhibit consistency across sessions and can be used to record PA and ESE among PwP. However, there are limitations, particularly for higher PA levels. MDC