Abstract:[Objective] To explore the incidence and related factors of cerebrospinal fluid leakage (CSFL) in posterior total laminectomy for decompression of thoracic ossification ligamentum flavum to provide a reference for clinical prevention of CSFL. [Methods] A retrospec- tive cohort study was conducted on patients who received posterior total laminectomy for decompression of thoracic ossification of ligamen- tum flavum between August 2015 and August 2021. According to whether CSFL happened, the patients were divided into the CSFL group and non-CSFL group. The univariate comparison, and multiple binary logic regression were conducted to search the factors related to CSFL. [Results] Of the 108 patients included in this study, 28 patients had CSFL, accounting for 25.93%. In term of univariate comparison, the CS- FL group had significantly higher ratio of preoperative limb paralysis (P<0.05); significantly less residual rate of spinal canal area, the residu- al rate of diameter of the canal on the midline and the residual rate of the sagittal diameter on the images (P<0.05); additionally, significantly higher ratio of intraoperative conventional bone chisels used (P<0.05), significantly more number of segments involved (P<0.05), as well as significantly longer operation time and hospital stay than the non-CSFL group (P<0.05). However, there were no significant differences be- tween the two groups in age, gender, BMI, course of disease, bladder and bowel dysfunction, preoperative JOA score, drinking history, smok- ing history, preoperative comorbidities, such as hypertension, diabetes, Sato classification, MRI grade, residual rate of transverse and antero- posterior diameter, residual rate of paramedian diameter and surgical site (P>0.05). As result of logistic regression, the more segments in- volved (OR=4.272, P=0.007) and small residual rate of spinal canal area (OR=0.903, P<0.001) was an independent risk factor for CSFL. [Conclusion] More thoracic segments involved and less residual rate of spinal canal area are associated with higher risk of CSFL. The corre- sponding measures should be taken to reduce the occurrence of CSFL.