BACKGROUND The clinical diagnosis of idiopathic Parkinson's disease (iPD) can be challenging. In these cases, additional diagnostic methods are available that can help to improve diagnostic accuracy. This article provides an overview of currently available and promising novel ancillary methods for the early and differential diagnosis of iPD. RESULTS Imaging tools, such as 1.5 Tesla magnetic resonance imaging (MRI) and computed tomography (CT) are mainly used for the differentiation between iPD and symptomatic parkinsonian syndromes (PS). High-resolution diffusion tensor imaging and iron and neuromelanin-sensitive high-field MRI sequences can become important in the future, particularly for earlier diagnosis. Transcranial B‑mode sonography of the substantia nigra and basal ganglia is established for early and differential diagnostics, especially in the combination of diagnostic markers but necessitates an adequately trained investigator and the use of validated digital image analysis instruments. DATScan can discriminate iPD from essential tremor, medication-induced parkinsonism and psychogenic movement disorder but not iPD from atypical PS. For the latter differential diagnosis, fluorodeoxyglucose positron emission tomography and myocardial metaiodobenzylguanidine scintigraphy can be helpful. Olfactory testing should preferably be used in combination with other diagnostic tests. Genetic, biochemical and histopathological tests are currently not recommended for routine use. Novel sensor-based techniques have a high potential to support clinical diagnosis of iPD but have not yet reached a developmental stage that is sufficient for clinical use. Novel sensor-based techniques have high potential to support clinical diagnosis of iPD, but have not yet reached a development stage that is sufficient for clinical use. CONCLUSIONS Ancillary diagnostic methods can support the early and differential diagnosis of iPD.