BACKGROUND: Parkinson's disease is a progressive neurodegenerative disorder in which non-motor psychiatric symptoms are common. Anxiety disorder is associated with poorer clinical outcomes and reduced quality of life in Parkinson's disease, yet population-based evidence on the risk of newly diagnosed anxiety disorder after Parkinson's disease remains limited. METHODS: We conducted a nationwide population-based matched cohort study using data from the Korean National Health Insurance Service between 2012 and 2023. Incident Parkinson's disease was identified using diagnostic codes, and anxiety disorder was defined based on repeated clinical diagnoses. Individuals with a prior history of anxiety disorder were excluded using a three-year washout period. Patients with Parkinson's disease were matched to general population controls at a 1:5 ratio using propensity scores. Incidence rate ratios and adjusted hazard ratios were estimated using time-stratified Cox regression models. RESULTS: The study included 3,742 patients with Parkinson's disease and 18,710 matched controls. The incidence rate of anxiety disorder was higher among patients with Parkinson's disease than among controls (56.62 vs. 28.10 per 1,000 person-years), corresponding to an incidence rate ratio of 2.01. The increased risk was most pronounced during the first three years after diagnosis and again during long-term follow-up, indicating a time-dependent pattern. CONCLUSION: Patients with Parkinson's disease experience a substantially higher incidence of anxiety disorder compared with the general population, with risk varying over the disease course. These findings highlight anxiety disorder as an important non-motor psychiatric manifestation of Parkinson's disease and support the need for longitudinal mental health monitoring in this population.