This study aimed to evaluate the internal consistency and factor structure of the Oswestry Disability Index (ODI) among patients undergoing lumbar spinal surgery. The sample included 1,515 patients who underwent lumbar spinal surgery at a university hospital between 2018 and 2021. Cronbach’s alpha was used to assess internal consistency, and exploratory and confirmatory factor analyses were conducted to evaluate the factor structure. The average age of the patients was 58.5 years, with 53% being women. The mean ODI score was 43.4%. The internal consistency of the ODI was good, with an alpha of 0.87. Exploratory factor analysis revealed a unidimensional structure, and item loadings on this factor were moderate to substantial for all 10 items. One-factor confirmatory factor analysis demonstrated an acceptable fit, with correlations between the main factor "disability" and individual items ranging from moderate (0.44) to substantial (0.76). The highest correlations were observed for items "traveling," "social life," and "sex life," while the lowest correlation was for the item "standing." The study concluded that the ODI is a reliable and valid unidimensional scale for assessing disability severity in patients undergoing lumbar spinal surgery. In the studied population, "traveling," "social life," "sex life," and "personal care" were the most important items, while "walking" and "standing" were the least important. However, the generalizability of these results may be limited by the heterogeneity and modest size of the studied cohort.This study aimed to evaluate the internal consistency and factor structure of the Oswestry Disability Index (ODI) among patients undergoing lumbar spinal surgery. The sample included 1,515 patients who underwent lumbar spinal surgery at a university hospital between 2018 and 2021. Cronbach’s alpha was used to assess internal consistency, and exploratory and confirmatory factor analyses were conducted to evaluate the factor structure. The average age of the patients was 58.5 years, with 53% being women. The mean ODI score was 43.4%. The internal consistency of the ODI was good, with an alpha of 0.87. Exploratory factor analysis revealed a unidimensional structure, and item loadings on this factor were moderate to substantial for all 10 items. One-factor confirmatory factor analysis demonstrated an acceptable fit, with correlations between the main factor "disability" and individual items ranging from moderate (0.44) to substantial (0.76). The highest correlations were observed for items "traveling," "social life," and "sex life," while the lowest correlation was for the item "standing." The study concluded that the ODI is a reliable and valid unidimensional scale for assessing disability severity in patients undergoing lumbar spinal surgery. In the studied population, "traveling," "social life," "sex life," and "personal care" were the most important items, while "walking" and "standing" were the least important. However, the generalizability of these results may be limited by the heterogeneity and modest size of the studied cohort.