BackgroundObesity is a possible factor which affects severity of symptoms and disease activity in fibromyalgia syndrome (FMS). The aim of our study was to determine the association between body mass index (BMI) and pain, tender point count (TPC), disease activity, anxiety and depression in patients with FMS.MethodsThis was a descriptive study. A total of 124 female FMS patients between 18 and 55 years of age were enrolled. FMS patients were evaluated with visual analog scale (VAS), fibromyalgia impact questionnaire (FIQ), Hamilton anxiety scale (HAM-A) and Hamilton depression scale (HAM-D). Patients were divided into three groups according to BMI levels: normal weight, overweight and obese. Normal weight was defined as BMI 18.5–24.9, overweight as BMI 25.0–29.9 and obesity as BMI ≥ 30. We assessed the BMI status and its association with symptom severity in patients with FMS.ResultsSignificant differences were detected in VAS, TPC, FIQ and HAM-D among the groups (p < 0.05). There were no significant differences between the groups in HAM-A (p = 0.328). The highest scores were found in the obese group. Significant positive correlations were determined between BMI levels and VAS, TPC, FIQ and HAM-D (r = 0.277, p = 0.002; r = 0.384, p < 0.001; r = 0.292, p = 0.001; r = 0.357, p < 0.001).DiscussionObese female FMS patients had higher levels of pain, TPC, disease activity and depression. BMI was significantly and positively correlated with clinical manifestations of FMS. Therefore, FMS treatment programs should include weight loss strategies.