Given the increasing recognition that neurodegeneration begins decades before the appearance of motor symptoms of Parkinson disease (PD), recent attention has turned to methods of preclinical or prodromal diagnosis. Accurate preclinical diagnosis of individuals at high risk of developing manifest motor PD can improve clinical counseling as well as provide an enriched cohort for studies of possible disease-modifying therapies. In this review article, the authors synthesize the myriad clinical, radiographic, and biochemical signatures of preclinical PD, with an emphasis on biomarkers that may provide accurate population screening for the disease. As individual biomarkers have relatively lowsensitivity and specificity, any population-based approach to preclinical diagnosis will likely combine multiple biomarkers to improve both negative and positive predictive value. •The long latent period of Parkinson disease (PD) provides an opportunity for early diagnosis and possible intervention.•Clinical, radiographic, and biochemical signatures of latent PD can be used to identify those at high risk of PD.•Early diagnosis will improve prognostic counseling and provide an enriched cohort for trials of disease-modifying therapies.