Purpose <p>The purpose of this study was to investigate the association between body mass index (BMI) and changes in pain scores among elderly patients with chronic pain. The pain disability assessment scale (PDAS) and the pain catastrophizing scale (PCS) were employed as assessment tools.</p> Methods <p>A single-center, retrospective cohort study was conducted at a university hospital multidisciplinary pain center from 2017 to 2020, involving 180 patients aged ≥ 65 years with noncancer pain persisting for at least 3 months. Patients were classified into three groups according to BMI: low (BMI &lt; 18.5), standard (18.5 ≤ BMI &lt; 25), and high (BMI ≥ 25). Initial, 3-month, and 6-month PDAS and PCS scores were collected and analyzed using mixed-effects models.</p> Results <p>No significant differences were observed in PDAS scores across BMI groups. However, PCS scores were significantly higher in the low BMI group. Furthermore, no significant differences were detected in PDAS and PCS scores based on the interaction between BMI group and time point (month).</p> Conclusion <p>Among elderly patients with chronic pain, the low BMI group exhibited a significantly higher PCS score, while PDAS scores did not vary based on the BMI group. No differences were detected in treatment-related changes over time across BMI groups.</p>