AIM: To reveal the reliability and validity of the Turkish Lumbar Spine Instability Questionnaire for evaluating patients with lumbar instability and low back pain. MATERIAL and METHODS: A total of 100 patients with low back pain participated in the study. Test-retest and internal consistency analyses were used to assess the reliability of the questionnaire, and correlation analysis was used to determine its validity. For correlation analysis, the total scores of the Lumbar Spine Instability Questionnaire, Visual Analog Scale, Bournemouth Questionnaire, Tampa Scale of Kinesiophobia, and Roland Morris Disability Questionnaire were compared. RESULTS: Reliability analysis showed that the internal consistency value of the questionnaire was 0.818, and the intraclass correlation coefficient (ICC) value was 0.839. Pearson correlation analysis showed that the questionnaire had a good correlation with the Tampa Scale of Kinesiophobia (0.520) and a stronger correlation with the Visual Analog Scale (0.702), Roland Morris Disability Questionnaire (0.767), and Bournemouth Questionnaire (0.667). CONCLUSION: Our results confirmed that the Turkish version of the Lumbar Spine Instability Questionnaire is reliable and valid.