Viral infections, especially recurrent viral infections in childhood are a well-known risk factor of bronchial hyperresponsiveness and the development of asthma and COPD. The aim of this review was description of the possible role of viruses in the pathogenesis of obstructive lung diseases. Even though a lot of mechanisms in which viruses induce asthma and obstructive lung disease remain unclear, the role of viruses seems to be undeniable. Respiratory syncytial virus--a common cause of childhood bronchiolitis--is a risk factor for the development of atopy, asthma and allergy. The risk is increased in children with familial history of asthma. The reason is that RSV stimulates Th2 pattern of immune response, which is similar to inflammation, found in asthmatic patients. A significant role in the pathogenesis of COPD is related to recurrent viral infections that may be the answer why CD8+ cells predominate in bronchial inflammation in patients with COPD. Latent adenoviral infection is probably important in the pathogenesis of obstructive disease. The E1A region of adenoviral genome and adenoviral E1A protein can be found in epithelial cells long after acute infection resolves. It is well known that in patients with COPD, E1A protein can be detected more often than in healthy subjects and it is responsible for amplifying the response to cigarette smoke and inducing steroid resistance.