We postulate that most patients with chronic cough have a single discrete clinical entity: cough hypersensitivity syndrome. We constructed a questionnaire that elicits the major components of the syndrome. Here we describe the validation of this questionnaire. Following iterative development, the Hull Airway Reflux Questionnaire (HARQ) was administered to patients and normal volunteers. It is self-administered and comprises 14 items with a maximum score of 70. Unselected patients were recruited sequentially from the Hull Cough Clinic. Preclinic questionnaires were compared with those obtained at the clinic. Responsiveness was assessed 2 months after the clinic visit. One hundred eighty-five patients and 70 normal volunteers were included in this study. There was a marked difference in HARQ scores between patients with chronic cough and normal volunteers. The sensitivity (94%) and specificity (95%) of the HARQ was high, with an area under the ROC curve of 0.99. All items of the scale significantly correlated positively with others in the scale and with the total score. On repeatability testing using Cohen's kappa with quadratic weights, significant agreement was noted for all items. Good correlation was observed between the total scores (r = 0.78). The questionnaire was also responsive to treatment; the minimum clinically significant change was estimated to be 16 points. We have demonstrated the HARQ to have good construct and criterion validity. It is both reproducible and responsive to change. It can be used as a diagnostic instrument and demonstrates that chronic cough represents a single coherent entity: cough hypersensitivity syndrome.