Objectives Restless legs syndrome (RLS) symptoms are common in Multiple Sclerosis (MS) patients. The aim of the current study was to examine for the first time whether RLS could affect the functional capacity and various contributing parameters related to quality of life and fatigue in MS patients. Methods According to their RLS status, 50 relapsing-remitting MS patients were divided into the RLS (n = 10) and non-RLS groups (n = 40). Specific questionnaires were used in order to assess the health-related quality of life (HRQoL), fatigue levels, sleep quality, daily sleepiness, and depression symptoms of the patients. Functional capacity was examined using a battery of functional tests. Total body and visceral fat levels were assessed via bioelectrical impedance analyzers. Results Sleep quality, depression, fatigue, and HRQoL levels were found to be significantly worse in the patients with RLS compared to their free-RLS counterparts (P < 0.05). In addition, patients with RLS were found to exhibit further impairments in their performance in various functional tests related mainly with strength levels of lower extremities (P < 0.05). Finally, the patients with RLS were found to have significantly higher both total and trunk fat levels compared to patients without RLS (P < 0.05). A strong correlation was observed between the severity of RLS symptoms, sleep quality, fatigue, and QoL levels. Discussion It seems that RLS contributes even further to impairments on sleep quality, fatigue, functional capacity, and therefore HRQoL levels in relapsing-remitting MS patients, whilst for the first time a link between high fat levels has been revealed.