To determine whether cognitive dysfunction and depression are more prevalent in restless leg syndrome (RLS) subjects compared to controls and the impact of RLS severity on these variables. A prospective study was performed on 681 subjects (161 with RLS). The RLS group was subdivided into three subgroups of mild, moderate and severe based on International RLS Study Group (IRLSSG) score. General linear regression adjusted for age, sex and education was performed to evaluate for association between controls, RLS subgroups and outcomes. Analysis of cognitive functioning demonstrated a significant difference between controls and severe RLS subgroup for AVLT long term memory (p=0.01), Stroop Word (p=0.003), Stroop Color (p<0.001), Stroop Word/Color (p=0.001) and judgement of line orientation (p=0.006). When these were adjusted for Epworth Sleepiness Scale (ESS), there was reduced effect size with significant differences still noted for Stroop Word/Color(p=0.011) and Judgement of Line Orientation (p=0.006). The ESS mean (SD) score was 5.7 (4.2) in controls, 7.2 (4.6) for mild RLS, 7.5 (4.0) for moderate RLS and 9.3(5.2) for severe RLS. Only the severe RLS group showed a significant difference in ESS compared to control (p<0.001). Also noted was a significant difference in depression as measured by HAM-D and the Geriatric Depression Scale (p <0.001 for both) between the severe RLS subgroup and controls. This study found reduced performance in executive function and visuospatial domains of cognitive testing in severe RLS. Our data demonstrates increased rating scale scores for depression and higher daytime sleepiness among those with severe RLS compared to controls.