BACKGROUND: Parkinson's disease (PD) is marked by pervasive uncertainty due to fluctuating motor and non-motor symptoms, variable treatment response, and an unpredictable clinical course. Intolerance of uncertainty (IU), a tendency to perceive ambiguity as threatening and respond with worry, avoidance, or decisional paralysis, may be consequential in PD, yet lacks a PD-focused synthesis. OBJECTIVE: To synthesize conceptual, qualitative, and emerging quantitative literature on IU in idiopathic PD, describe clinical and psychosocial correlates across the illness trajectory, and identify implications for assessment and intervention. METHODS: This targeted narrative review searched MEDLINE (PubMed), Embase, PsycINFO, and Web of Science from inception to May 22, 2025, supplemented by reference screening and Parkinson's disease conference or guidance sources. English-language empirical and clinically informative papers addressing intolerance of uncertainty (IU) or closely related uncertainty constructs in adults with idiopathic PD and/or care partners were appraised at title/abstract and full-text levels, then charted for narrative synthesis. RESULTS: Across qualitative, quantitative, intervention, and clinical review/guidance papers, symptom unpredictability, treatment uncertainty, identity disruption, shame, and future-planning concerns were linked with anxiety, demoralization, avoidance, reduced participation, and poorer quality of life. CONCLUSION: IU may be a modifiable, common underlying pathway through which PD-related unpredictability, potentially influenced by dopaminergic, executive, and stress-system vulnerabilities, contributes to sustained psychological and functional burden. Advancing PD-sensitive measurement and testing IU-targeted interventions within multidisciplinary care models may improve adjustment and quality of life for patients and caregivers.