OBJECTIVES: The purpose of this study was to investigate the clinical characteristics and incidence of restless legs syndrome (RLS) in outpatients with psychiatric illness. METHODS: 146 adult patients (male 52, female 94) were selected from those who visited a psychiatric outpatient clinic. RLS was evaluated through an interview method using diagnostic criteria and a severity rating scale for RLS developed by the International RLS Study Group (IRLSSG). The authors also applied Beck's Depression Inventory (BDI), Beck's Anxiety Inventory (BAI), the Pittsburgh Sleep Quality Index, Barnes Akathisia Rating Scale and neurological examination. RESULTS: Thirty-four (23.3%) among 146 subjects were diagnosed as having RLS. Fifteen (44.1%) among those 34 RLS patients reported to have developed their RLS after starting their psychotropic agents and only 4 patients (11.7%) had currently been receiving treatment for their RLS. The RLS group showed higher BDI and BAI scores (p<0.01) and lower sleep quality (p<0.01) compared to those of non-RLS. The RLS group also showed a significantly higher co-morbidity of parasomnias (chi-square =8.5, p<0.01) and peripheral neuropathy (chi-square =5.2, p<0.05). CONCLUSION: The results from this study suggest that a substantial proportion of outpatients with psychiatric illness are suffering RLS. Our data suggest that clinicians should pay attention to the possible presence of RLS among their patients who are taking psychotropic agents.