Current diagnostic modalities in Parkinson's disease (PD) are limited by the fact that they identify PD by the presence of motor symptoms; by this point, over 60 percent of all dopamine neurons within specific regions of the basal ganglia may have been lost. Nonmotor symptoms manifest in PD long before motor symptoms, and the early presence of nonmotor symptoms offers an opportunity for early diagnosis and early treatment of PD, with consequent benefits to patient quality of life and potential treatment cost savings. Numerous different premotor symptoms have been identified; diminished olfactory function and REM behavioral sleep disorders (RBDs) may be particularly suitable for the purposes of early diagnosis. Olfactory testing, while in itself not specific for PD, has been shown to offer very high degrees of sensitivity and specificity in distinguishing PD from healthy controls and from other forms of parkinsonism, particularly when accompanied by other means of detection, such as sonography, motor symmetry evaluation, and magnetic resonance imaging (MRI)/diffusion tensor imaging. Biological biomarkers--including protein panels and autoantibody testing--have demonstrated excellent diagnostic capacity, and a recently identified 5-gene panel has been shown to have high specificity and sensitivity in distinguishing early PD from healthy controls and advanced PD. Increasingly sophisticated neuroimaging techniques are also proving capable of early PD detection and differentiation from other parkinsonian types. These recent developments in PD diagnosis underscore the necessity of rethinking what PD is and how, and when, it can be diagnosed.