Introduction: Patient-reported outcome measures (PROMs) are the preferred outcomes measured in patients with lumbar spinal degenerative diseases. As PROMs can be lengthy and therefore pose a burden to patients and researchers, short and standardized PROMs are needed, such as the Core Outcome Measures Index (COMI). Research question: Is the Dutch version of the COMI-back a reliable and responsive PROM to measure outcomes in lumbar degenerative spinal surgery? Methods: After translating and cross-cultural adapting the COMI-back into Dutch, patients who were on the waiting-list for lumbar decompression surgery in a secondary referral center, were enrolled in the validation study. Patients completed a baseline booklet consisting of the COMI-back, likert scales measuring back and leg pain, the Roland-Morris Disability questionnaire, the EuroQoL-5 dimensions and the WHO-Quality-of-Life-BREF questionnaire to test construct validity. Within 2 weeks and before undergoing surgery, patients completed the COMI-back again, to measure test-retest stability. Three months after surgery, a global treatment outcome (GTO) question and the COMI-back were completed to test responsiveness. Results: The COMI-back was successfully translated and adapted into Dutch. One-hundred-thirty-five patients completed the baseline booklet, 93 the test-retest questionnaire and 102 the responsiveness questionnaire. The COMI-summary score and four of five COMI-domains, showed good to very good correlation to the reference questionnaires (ρ > 0.41). The COMI-back showed a good test-retest stability with an intraclass correlation coefficient of 0.81 for the summary score. Furthermore, the standard error of agreement was 0.65 and the minimal detectable change was 1.8 points. The ROC-curve showed an area under the curve of 0.89 (95% CI 0.82 to 0.95). Conclusion: The Dutch version of the COMI-back has satisfactory psychometric properties and is a reliable and responsive patient-reported outcome measure in patients undergoing surgery for lumbar ...