OBJECTIVES. The aim of this study was to conduct the cross-cultural adaptation of Neck Disability Index (NDI) and investigate the validity and reliability of Turkish version in patients with neck pain. SUMMARY OF BACKGROUND DATA. The NDI is a reliable evaluation instrument for disability but there are no published Turkish version. METHODS. Eighty-eight patients with neck pain for at least 3 months were included in the study. NDI, The Neck Pain and Disability Scale and Visual Analogue Scale (VAS) were completed by all subjects. Test-retest reliability was determined by using intraclass correlation coefficient and Pearson's correlation analysis. For the determination of concurrent validity, the relation between NDI and VAS was examined by Pearson's correlation analysis and for the determination of construct validity, the relation between NDI and Neck Pain and Disability Scale was investigated. RESULTS. Intraclass correlation coefficient score for test-retest reliability was 0.979 (95%, confidence interval = 0.968-0.986). For concurrent validity, the relation between NDI and VAS was investigated, the r value for test and retest was 0.508 and 0.620, respectively (P < 0.0001). For construct validity, the relation between NDI and the Turkish version of NPDA was investigated, the r value for test and retest was 0.659 (P < 0.0001) and 0.728 (P < 0.0001), respectively. CONCLUSION. The Turkish version of NDI was found to be a valid and reliable method of measurement for evaluating disability, caused by problems of the neck region as it is easy to comprehend by the patients and the time needed to apply is short in clinics. © 2008 Lippincott Williams & Wilkins, Inc.