The purpose of this study was to determine reliability and validity of the Neck Disability Index (NDI) now in use for the first time in neck pain patients of Korea. Fifty subjects (26 males and24 female) with neck pain enrolled in the study. They completed a standardized self-administered questionnaire that include pain intensity, personal care, lifting, reading, headaches, concentration, work, driving, sleeping and recreation. Reliability was determined by intra-class correlation coefficient (ICC) and Cronbach's alpha by internal consistency. Validity was examined by correlating the NDI scores to the Visual Analog Scale (VAS) score. The Test-retest reliability of the translated versions of the NDI was good ICC (2,1) = .90 (95%CI .85 .95). Cronbach's alpha value for NDI was found to be .95 and this was statistically significant (p<.05). The criterion-related validity coefficients was .72 (p<.01). We conclude that the Korean version of NDI has shown to be a reliable and valid instrument for the assessment of neck pain.