Hallervorden-Spatz syndrome (HSS) is a degenerative neurologic disorder associated with progressive rigidity, dystonia, impaired voluntary movement, dysarthria, and mental deterioration. Pathologically, there is iron deposition in the basal ganglia, with destruction of basal ganglia output neurons. Recent advances in the understanding of basal ganglia functional anatomy and physiology make it possible to hypothesize how specific neural mechanisms relate to specific clinical manifestations of HSS. Experimental lesions of the basal ganglia output nucleic cause involuntary muscle contractions, similar to contractions observed in dystonia. A model of selection and suppression of competing motor patterns by the basal ganglia is presented in relation to the manifestations of damage to basal ganglia output neurons. It is hypothesized that the dystonia and other motor abnormalities seen in HSS can be attributed to degeneration of basal ganglia output neurons.