Many different disorders have dystonia as the only or primary sign. The list of causes for dystonia increases yearly and now includes three mapped loci for primary torsion dystonia, although other susceptibility genes are suspected. Study of one of these primary torsion dystonia loci (DYT1) has culminated in the cloning of a gene which codes for a novel protein, torsin A. Physiological and positron emission tomography analyses suggest that dystonia results from impaired inhibition at cortical and subcortical levels; these physiological changes may in turn be due to striatal dysfunction and a mismatch or imbalance between the direct and indirect pathways. Future study of normal and mutant torsin A, as well as the identification of other primary torsion dystonia genes, should help elucidate the mechanisms underlying dystonia.