The aim of this study was to evaluate the causes of prolonged cough in a patient population referred to a chest clinic during a single year. One hundred and ninety-eight patients (11%) of the total yearly 1745 adult admissions fulfilled our criteria of prolonged cough. Asthma, suspicion of asthma and postnasal drip were the commonest causes of prolonged cough in 147 patients with normal chest roentgenograms (26%, 9% and 16%, respectively), and in 45% the cough was of unexplained origin. Nonspecific bronchial hyperreactivity was common in this latter group of patients probably due to a previous respiratory infection. Lung cancer (37%), tuberculosis (16%), sarcoidosis (16%), and allergic alveolitis (9%) were the most important findings in patients with abnormal chest roentgenograms.