A new computational method for quantification of tremor and other aspects of motor dysfunction is described. By using a digitizing tablet connected to a microcomputer, this analysis is derived from the handwritten Archimedean spiral. This technique extends the standard clinical neurologic test of spiral drawing into an objective and accurate measure that can automatically detect, characterize, and quantify motor dysfunction in patients with movement disorders. Further, it is safe, inexpensive, fast, portable, noninvasive, and can be administered to a large cohort of patients without the need for wires or other attachments. Spiral data are collected in the X, Y, and pressure axes, providing virtual "triaxial" recordings. Spiral analysis is shown to be capable of assessing subtle motor abnormalities potentially indicative of clinical problems in their earliest stages, and thus allow the most rational forms of genetic testing, treatment, or prevention. Spiral analysis may be useful as an initial marker of clinical involvement or serve as an objective gauge of change after therapeutic intervention.