Hemiatrophy has been reported in association with a variety of neurologic conditions, including parkinsonism. Patients with the hemiparkinson-hemiatrophy syndrome (HP-HA) have asymmetric parkinsonism with limb atrophy on the more affected side. Several authors have suggested that asymmetric brain damage early in life results in both atrophy and parkinsonism. Dopa-responsive dystonia (DRD) is a disease in which a deficiency of tetrahydrobiopterin, or, less commonly, of tyrosine hydroxylase, results in levodopa-responsive dystonia with parkinson features in children. We have recently identified four patients with DRD who had asymmetric dystonia and limb atrophy on the more affected side. Based on these patients, we suggest that a deficiency of the nigrostriatal dopamine system may, by itself, be sufficient to cause body atrophy and may underlie the limb atrophy in both DRD and HP-HA.