Dystonia is diagnosed based on its clinical features. Primary dystonia is separated from secondary dystonia by the absence of additional neurological abnormalities and the lack of possible acquired cause. Laboratory testing in primary dystonia is of minimal usefulness but essential in the evaluation of secondary dystonia, or dystonia with atypical features. In primary dystonia, there are no abnormalities on MRI or computerized tomography scans. In secondary dystonia, the MRI findings vary with the etiology. In patients with early-onset dystonia (<26 years of age) or late onset but with an affected relative with early-onset dystonia, DYT1 gene testing is indicated with appropriate genetic counseling. Currently, testing for other genetic loci is not available for clinical use.