The aim of this study was to investigate the associations between obesity and fibromyalgia syndrome (FMS). This study was conducted at the University of Utah Pain Management and Research Center, Salt Lake City, Utah. Thirty-eight FMS patients were included in this study. Neuroendocrine indices (catecholamines, cortisol, C-reactive protein [CRP], and interleukin-6), symptom measures (Fibromyalgia Impact Questionnaire), sleep indices (Actigraph), and physical functioning (treadmill testing) were measured. Body mass index (BMI) provided the primary indicator of obesity. Approximately 50% of the patients were obese and an additional 21% were overweight. Strong positive associations were found between BMI and levels of IL-6 (r = 0.52) and epinephrine (r = 0.54), and somewhat weaker associations with cortisol (r = 0.32) and CRP (r = 0.37). BMI was also related to maximal heart rate (r = 0.33) and inversely related to distance walked (r = −0.41). BMI was associated with disturbed sleep: total sleep time (r = −0.56) and sleep efficiency (r = −0.44). No associations between self-reported symptoms and BMI were found. This study provides preliminary evidence suggesting that obesity plays a role in FMS-related dysfunction.