The infectious complications after lung transplantation have been studied in 26 patients suffering from mucoviscidosis who had transplants in the Ile-de-France between July 1987 and October 1990. We counted 99 infections (74 bacterial infections, 23 viral infections and two fungal infections) during a cumulative observation period of 127 months. The majority of the infections (48%) were localised to the grafted lung. These infections were responsible for 61% of deaths (50% secondary to bacterial infections and 11% to viral infections). The risk of infection remains even after a considerable time after transplantation in this series. These studies underline the importance of infectious complications in the mortality and morbidity of lung transplant patients suffering from mucoviscidosis.