We have carried out a case-control survey of the prevalence of restless legs syndrome (RLS) in 118 Parkinson's disease out-patients with different stage of disease severity by using the International restless legs syndrome Study Group clinical criteria. This study failed to demonstrate a significantly augmented prevalence of either primary and secondary restless legs syndrome pooled together or primary restless legs syndrome alone among Parkinson's disease patients as compared to age and gender matched controls. The results of our survey do not confirm a significant co-morbid occurrence of the two disorders. However, an unavoidable limitation of this and all previous studies is that most of the patients examined were already treated with dopaminomimetic drugs, which could have abolished a mild unrecognized RLS anteceding the diagnosis of Parkinson's disease or possibly masked the subsequent emergence of the sensory-motor disorder following the onset of Parkinson's disease.