A prospective cohort study with a 1 week follow-up. To examine the reliability and responsiveness of the Dutch version of the Neck Disability Index (NDI) in patients with acute neck pain in general practice. An increasing number of studies on treatment options is published in which the NDI is used. Reports of the ability of the NDI to detect change over time, often called responsiveness, however have not yet been published. At baseline 187 patients (119 women, 68 men) were included. They completed a questionnaire on demographic variables, self-reported cause of their complaints and the NDI. After 1 week, 86 patients were sent the NDI again together with the perceived recovery scale which was used as our external criterion. The scale ranged from 1 (complete recovery) to 7 (complaints are worse than ever). Response rate was 93%. Test-retest scores on reliability were good (ICC = 0.90). A Bland and Altman plot and a graph of total sum score differences showed no visible tendency towards unequal spreading of the data. For patients that reported on the perceived recovery scale that they were "stable" we found a responsiveness ratio of 1.82. The standard error of measurement (SEM) was 0.60 what resulted in a minimal detectable change (MDC) of 1.66. The NDI has shown to be a reliable and responsive instrument in patients with acute neck pain in general practice.