Parkinson's disease is a common movement disorder associated with considerable disability. The clinical syndrome of parkinsonism is based on the presence of core clinical features of rest tremor, bradykinesia, rigidity and impaired postural reflexes or gait. Parkinsonism is most often caused by Parkinson's disease, but can also be caused by other disorders, including cerebrovascular disease, multiple-system atrophy, progressive supranuclear palsy and other disorders. Parkinsonism can be identified by questionnaires and confirmed in person or by videotaped clinical examinations. The identification of presymptomatic cases remains problematic but is motivated by the hope for treatment before symptoms appear. Quantitative approaches to the diagnosis of parkinsonism based on the measurement of the cardinal features are available. Clinical approaches should include identification of features atypical for Parkinson's disease, which exclude the diagnosis, and documentation of a response to dopaminergic medications, which support a diagnosis of Parkinson's disease. Loss of smell and visual dysfunction are found in early patients and may be useful in screening protocols. In addition, behavioral changes, including depressive symptoms, may be detected in presymptomatic cases. Cognitive changes, such as impaired set shifting, have been observed in early Parkinson's disease, but can be seen with other causes of parkinsonism. Neuroimaging techniques, including positron emission tomography or single-photon emission computed tomography, are available to quantify dopaminergic neurons, while magnetic resonance imaging may be helpful in differentiating other forms of parkinsonism from Parkinson's disease. There are numerous approaches available to the identification of parkinsonism and Parkinson's disease. The gold standard remains a clinical diagnosis, confirmed by autopsy.