Background: Self-efficacy (SE) for managing chronic conditions is associated with self-reported health outcomes in patients with Parkinson’s disease (PD). SE may change over time, but there is a lack of understanding of the longitudinal relationship between SE and self-reported health outcomes and predictors of SE change. Objective: To examine if SE for managing chronic conditions in five subdomains (managing daily activities, managing emotions, managing medications and treatments, managing social interactions, and managing symptoms) was associated with patient-reported physical function (Aim1) and patient-reported mental health (Aim2) over three years among those with PD, and to examine predictors of three-year changes of SE in five subdomains (Aim3). Methods: Multiple linear regression models were constructed to analyze the longitudinal relationship between five subdomains of SE and both physical function and mental health, and to find predictors of three-year change in SE five subdomains. Results: Three-year change in patient-reported physical function was associated with baseline SE for managing daily activities and for managing medications and treatments. Also, a three-year change in anxiety was associated with SE for managing medications and treatments and for managing symptoms, while a three-year change in depression was associated with SE for managing emotion, for managing medications and treatments, and for managing symptoms. In all cases, higher baseline SE was associated with more favorable outcomes. Overall, SE for managing chronic conditions declined in all five subdomains over three years. The changes in SE for managing chronic conditions were predicted by the Hoehn and Yahr stage at baseline across subdomains. Conclusions: SE for managing chronic conditions was a significant predictor of three-year change in patient-reported outcomes in physical function, anxiety, and depression in PD, suggesting SE as a screening tool for long-term change in patients’ health status. Also, significant declines in SE for three years emphasize clinical attention. Overall, the findings suggest that SE is not only an important marker of future patient-reported outcomes but also a potentially modifiable target for intervention. Clinical strategies aimed at maintaining or enhancing SE in patients with PD may help mitigate functional and emotional deterioration over time.