AbstractBackgroundGastrointestinal dysfunction is an important feature of Parkinson's disease (PD), and there is increasing evidence that it may play a key role in the disease process. However, its assessment is limited by different tools and underlying differences in diagnostic criteria for gastrointestinal dysfunction. To date, there is no psychometric instrument for quantitative evaluation of gastrointestinal symptoms specifically designed for use in PD.ObjectiveThe objective of this study was to develop a self‐report questionnaire‐based instrument, the Gastrointestinal Dysfunction Scale for Parkinson's Disease, and to evaluate its psychometric properties.MethodsWe performed a literature review and conducted 3 focus groups to develop the Gastrointestinal Dysfunction Scale for Parkinson's Disease. Three hundred and sixteen patients with PD and 55 controls completed the Gastrointestinal Dysfunction Scale for Parkinson's Disease, the Non‐Motor Symptom Scale, the Hospital Anxiety and Depression Scale, and a stool diary adapted from the Bristol Stool Chart.ResultsThe Gastrointestinal Dysfunction Scale for Parkinson's Disease demonstrated good internal consistency (Cronbach's α = 0.82) and test–retest stability (0.79 < ICCs > 0.94). Correlation analyses supported good convergent and divergent validity. Receiver operating characteristic analysis demonstrated that a cutoff score of ≥9 on the Gastrointestinal Dysfunction Scale for Parkinson's Disease Constipation subscale discriminates between PD patients with and without constipation.ConclusionsThe Gastrointestinal Dysfunction Scale for Parkinson's Disease is a novel disease‐specific self‐report tool to quantitatively assess the presence and severity of gastrointestinal dysfunction features in patients with PD, with strong reliability and validity. Further longitudinal studies are needed to demonstrate its utility in tracking gastrointestinal dysfunction in PD clinical cohorts. © 2021 International Parkinson and Movement Disorder Society