The MDS Research Criteria for Prodromal Parkinson's Disease were developed to define and diagnose early stages of Parkinson's disease (PD) before the onset of full clinical symptoms. These criteria are based on probability and use a Bayesian naive classifier to estimate the likelihood of prodromal PD. Prodromal PD refers to the stage where early symptoms or signs of neurodegeneration are present, but a full clinical diagnosis of PD is not yet possible. The criteria define three stages of PD: preclinical PD (no evident symptoms), prodromal PD (symptoms present but not sufficient for diagnosis), and clinical PD (diagnosed based on motor signs). The criteria incorporate risk factors, nonmotor symptoms, and diagnostic tests to estimate the probability of prodromal PD. Risk markers include factors like sex, occupational exposure to pesticides, caffeine use, and family history of PD. Prodromal markers include clinical nonmotor symptoms such as REM sleep behavior disorder, olfactory dysfunction, constipation, and erectile dysfunction, as well as motor abnormalities and neuroimaging findings. The criteria use likelihood ratios (LRs) to calculate the probability of prodromal PD based on prior probability and diagnostic information. A probable prodromal PD is defined as a likelihood of ≥80%. The criteria are intended for research purposes only, as there is currently no neuroprotective therapy for PD. They require continuous updating as new data become available. The criteria aim to provide a framework for identifying early stages of PD and may be used in future disease-modifying trials. Ethical considerations are important, as disclosing prodromal PD risk may have implications for patients' lives. The criteria are data-driven and rely on prospective studies to validate their predictive value. They are not intended for clinical use outside of research settings.The MDS Research Criteria for Prodromal Parkinson's Disease were developed to define and diagnose early stages of Parkinson's disease (PD) before the onset of full clinical symptoms. These criteria are based on probability and use a Bayesian naive classifier to estimate the likelihood of prodromal PD. Prodromal PD refers to the stage where early symptoms or signs of neurodegeneration are present, but a full clinical diagnosis of PD is not yet possible. The criteria define three stages of PD: preclinical PD (no evident symptoms), prodromal PD (symptoms present but not sufficient for diagnosis), and clinical PD (diagnosed based on motor signs). The criteria incorporate risk factors, nonmotor symptoms, and diagnostic tests to estimate the probability of prodromal PD. Risk markers include factors like sex, occupational exposure to pesticides, caffeine use, and family history of PD. Prodromal markers include clinical nonmotor symptoms such as REM sleep behavior disorder, olfactory dysfunction, constipation, and erectile dysfunction, as well as motor abnormalities and neuroimaging findings. The criteria use likelihood ratios (LRs) to calculate the probability of prodromal PD based on prior probability and diagnostic information. A probable prodromal PD is defined as a likelihood of ≥80%. The criteria are intended for research purposes only, as there is currently no neuroprotective therapy for PD. They require continuous updating as new data become available. The criteria aim to provide a framework for identifying early stages of PD and may be used in future disease-modifying trials. Ethical considerations are important, as disclosing prodromal PD risk may have implications for patients' lives. The criteria are data-driven and rely on prospective studies to validate their predictive value. They are not intended for clinical use outside of research settings.