We used single photon emission computed tomography (SPECT) to study striatal [123I]β-CIT binding and polysomnography to study periodic leg movements during sleep (PLMS) in eleven patients with idiopathic Parkinson's disease (PD). The reduced striatal [123I]β-CIT binding was significantly correlated with the number of PLMS. We propose that striatal dopaminergic nerve cell loss is involved in the increased number of PLMS in PD patients.