INTRODUCTION: To investigate the prevalence and characteristics of Restless Legs Syndrome (RLS) in patients with Behçet's Disease (BD) and Multiple Sclerosis (MS). METHODS: Consecutive patients with BD and MS seen in the outpatient clinic were included in the study. As a control group, volunteer subjects without a known peripheral or central nervous system disorder were included. The BD group was divided into two sub-groups as BD with neurological involvement [Neuro-Behçet's Disease (NBD)] and BD without any neurological involvement (other BD) for further evaluation. Data on demographic characteristics, medical history and family history were collected, and all patients underwent neurological examination. The patients were evaluated for the presence of diagnostic criteria for RLS. The features and severity of RLS were evaluated in patients with RLS using Restless Legs Syndrome Identification Form, and the International Restless Legs Syndrome Study Group (IRLSSG) Rating Scale. The clinical and radiological findings of patients with BD and MS were retrieved from their medical files. RESULTS: The study included a total of 96 patients with BD (mean age 39.9±11.8; 51 males; 41 patients with NBD) and 97 patients with MS (mean age 34.97±4.1 years; 24 males). There were 100 healthy control subjects (mean age 36.18±11.10 years; 46 males). RLS was more prevalent in MS (22.8%) and NBD (22%) groups compared to the control group (10%; p=0.004 and 0.029, respectively) with a statistically significant difference. The prevalence of RLS was higher in MS patients with less disability. Most severe RLS symptoms were observed in the MS group. The rate of sleep disorders was also higher in MS group. Although stress appeared to be a factor worsening RLS in all groups, its prevalence was higher in the MS group (p=0.011). There was no correlation between the distribution of magnetic resonance imaging lesions and RLS in both MS and NBD groups. CONCLUSIONS: It is well established that RLS can accompany disorders involving the peripheral and central nervous systems such as all types of peripheral neuropathy, myelopathy, and Parkinson's disease. The present study showed that MS and NBD also seem to be a risk factor for RLS, being associated with more severe symptoms.