For many years patients with chronic cough have been investigated in an attempt to diagnose the cause of the cough. Here I suggest that the overwhelming majority of patients with chronic cough have a single diagnosis: cough hypersensitivity syndrome. This is demonstrated by the homogeneous nature of the clinical history and investigational results of patients attending cough clinics. The hypersensitivity facet of the syndrome is demonstrated by objective testing with capsaicin and other protussive agents. Within the cough hypersensitivity syndrome there are different phenotypes. Those patients with a predominantly Th2-type immune response will develop eosinophilic inflammation and either cough-variant asthma or eosinophilic bronchitis. Those with predominantly heartburn symptoms will have a phenotype that reflects GERD and cough. However, the similarities between the different phenotypes far outweigh differences in a unifying diagnosis of the cough hypersensitivity syndrome, providing a more rational understanding of chronic cough.