Objectives To assess the association between physical fitness and fibromyalgia (FM) severity in women with FM as well as to assess whether different fitness components present an independent relation with FM severity. Design Population-based cross-sectional study. Setting University facilities and FM associations. Participants Women with FM (N=444). Interventions Not applicable. Main Outcome Measures FM severity was assessed with the Revised Fibromyalgia Impact Questionnaire (FIQR). Aerobic fitness (6-min walk test), muscle strength (handgrip, chair stand, and arm curl tests), flexibility (chair sit and reach and back scratch tests), and motor agility (8 foot Up and Go test) were measured with the Senior Fitness Test battery and digital dynamometry. A standardized composite score (hereafter “global fitness profile”) was calculated and divided into quintiles. Results Overall, physical fitness was significantly associated with the FIQR total and subscale scores, regardless of the fitness test used (all P<.05). The 6-minute walk and back-scratch tests were independently associated with the FIQR total score (R 2=.88; both P<.005). The group with the highest global fitness profile had 16% lower FM severity than did the group with the lowest global fitness profile (P<.001). Conclusions Our results suggest that higher physical fitness is consistently associated with lower FM severity in women with FM. Aerobic fitness and flexibility present independent associations with FM severity. However, the FIQR variability explained by these fitness tests was rather low (<10%), and further research on the potential disagreement between performance-based physical fitness and different self-reported outcomes in women with FM is warranted.