BACKGROUND: Symptoms, oesophageal pHmetry and proton pump inhibitor treatment are used for diagnosing gastro-oesophageal reflux-related cough. Weakly acidic reflux is now increasingly associated with reflux symptoms such as regurgitation or chest pain. AIM: To study the association between weakly acidic reflux and cough in a selected, large group of patients with unexplained chronic cough. METHODS: A total of 100 patients with chronic cough (77 'off' and 23 'on' a proton pump inhibitor) were studied using impedance-pHmetry for reflux detection and manometry for objective cough monitoring. Symptom Association Probability (SAP) Analysis characterized the reflux-cough association. RESULTS: Acid reflux could be a potential mechanism for cough in 45 patients (with either heartburn, high acid exposure or +SAP for acid reflux). Weakly acidic reflux could be a potential mechanism for cough in 24 patients (with either increased oesophageal volume exposure, increased number of weakly acidic reflux or +SAP for weakly acidic reflux). Reflux could not be identified as a potential mechanism for cough in 31 patients. CONCLUSION: A positive association between cough and weakly acidic reflux was found in a significant subgroup of patients with unexplained chronic cough. Impedance-pH-manometry identified patients in whom cough can be related to reflux that would have been disregarded using the standard diagnostic criteria for acid reflux.