Fibromyalgia syndrome (FMS) may cause functional disability, severe pain and fatigue and affect quality of life (QoL)which interfere with daily activities of patients. Aim: To determine the association between body mass index (BMI) and symptom severity, QoL and functional capacity in patients with fibromyalgia. Participants and Methods: Fifty women (50) with fibromyalgia and thirty (30) age matched healthy women control group   were assessed for BMI, socio-economic (SES) status  assessment and  clinical signs of  fibromyalgia by FMS-related measurements, visual analogue scale (VAS), number of tender points (NTP) Fibromyalgia Impact Questionnaire (FIQ) and Myalgia score. The short form health survey - 36, Functional capacity was conducted by six minute walk test. Results: The majority of patients were obese (74%): 48% class 1, 20% class 2, and 6 % class 3. Greater fibromyalgia-related symptoms and functional impairment were  found in the higher BMI group  with statistically significant differences regarding   SES   total score; education and culture total domain, NTP and myalgic score, 6 minutes' walk test, some domains of SF36 and leptin concentration. Severe FM showed higher VAS, NTP, Myalgic score, disease duration, BMI  and leptin concentration but  lower age and  SES than other grades with statistically  significant differences  regarding disease duration  VAS, myalgic score, leptin concentration and all  SF36 domains except general health perception. Conclusion and Recommendation: The findings support that excess weight is negatively related to QOL, functional capacity , SES but positively related to  disease severity (clinical and lab)  in women with FMS. A fibromyalgia treatment program needs to incorporate medical and behavioral weight loss programs for obese  patients