Obesity may influence fibromyalgia severity. The present study aimed to examine fibromyalgia (FM) symptomatology, quality of life (QoL), and functional capacity across obesity class categories. A total sample of 208 obese FM patients and 108 obese control women were included in the study. The sample was further categorized following the international criteria for obesity classes: obesity I (BMI 30.0-34.99 kg/m(2)), obesity II (BMI 35.0-39.99 kg/m(2)), and obesity III (BMI ≥40.0 kg/m(2)). QoL was assessed by means of the Short-Form-36 Health Survey (SF-36) and FM symptomatology with the Fibromyalgia Impact Questionnaire (FIQ). Standardized field-based fitness tests were used to assess cardiorespiratory fitness, muscular strength, flexibility, agility, and balance. All the dimensions of QoL, as measured by SF-36, were worse in obese FM patients compared to the obese control group (all p < 0.001). Obese FM patients also scored worse in the entire functional capacity tests studied (all p < 0.001). Except for the higher FIQ-depression across obesity status categories (p < 0.05), no differences between obesity status groups were found in QoL and FM impact. However, upper-body muscular strength and cardiorespiratory fitness were worse across obesity class categories and pairwise comparisons showed differences mainly between obesity I and II (p < 0.05, and p < 0.01, respectively). The absence of clear differences in QoL and FM symptomatology among obesity classes suggests that just avoiding any obese status may be a useful advice for a better management of the disease. Nevertheless, upper-body muscular strength and cardiorespiratory fitness, which are important health indicators highly related to the mortality risk, were worse across obesity categories.