Background <p>Obesity is recognized as a pathological condition characterized by excess body fat, which may be associated with impaired brain function, particularly with a reduction in attentional capacity. Fibromyalgia, a chronic rheumatic disorder, is marked by musculoskeletal pain, fatigue and sleep disturbances. When both obesity and fibromyalgia coexist, they worsen rheumatic symptoms and may contribute to cognitive decline. This study aimed to evaluate the association between cognitive function, body composition, and anthropometric indices in women with fibromyalgia.</p> Results <p>Exploratory, cross-sectional, correlational pilot study in 18 women with fibromyalgia. Sociodemographic and clinical characteristics, body composition, cognitive function, and variables related to mental health were examined. Body mass index, waist-to-hip ratio, and waist-to-height ratio were calculated. Spearman test was used to evaluate the correlation between body composition variables and cognitive function. The mean age was 44.4 ± 10.7&#xa0;years. 83.3% were overweight, 35.3% had a high percentage of fat, and 61.1% had a high cardiovascular risk. Regarding cognitive function, 72.2% presented probable cognitive impairment. Delayed recall was the only domain significantly correlated with body composition, showing inverse associations with fat mass (<i>r</i> = − 0.62; <i>p</i> = 0.004) and cardiovascular risk (<i>r</i> = − 0.49; <i>p</i> = 0.022).</p> Conclusion <p>Women diagnosed with fibromyalgia face significant cognitive impairment, as well as elevated levels of stress, anxiety, and depression associated with a state of excess malnutrition. Further research is suggested to validate and extend these findings and explore specific therapeutic interventions based on individualized care.</p>