Cough is one of the most common complaints causing patients to seek medical attention, and chronic cough, defined as a cough period of at least three weeks, accounts for more than a third of referrals to a chest physician. Cough is an important factor in the spread and survival of microorganisms, but until recently little attention has been given to Bordetella pertussis (B. pertussis) in patients with chronic cough. This review summarizes the B. pertussis diagnostic methods--culture--polymerase chain reaction (PCR), and serology--and surveys the literature on B. pertussis and chronic cough in adults. There is growing evidence that B. pertussis is an important cause of persistent cough in adults; thus prevalence of pertusssis of 12.4-26% has been reported in studies from US, Australia and Germany. Recently we found evidence of pertussis as the cause of chronic cough in 16% of otherwise healthy adults in Denmark. Therefore, patients with chronic cough should be examined for B. pertussis infection. The demonstration of B. pertussis in an adult patient with chronic cough has two advantages: 1) the patient can be reassured that symptoms will disappear spontaneously, why more or less invasive examinations and empirical therapeutic trials can be omitted, 2) the source of infection can be eradicated, and contact persons, particularly non vaccinated infants in whom pertussis might be very severe, can be treated in order to avoid or attenuate clinical symptoms.