A young competitive swimmer consulted a physician because of respiratory symptoms. He was found to have a normal spirometry. Bronchial asthma was diagnosed based on bronchial challenge test and appropriate treatment started. An overview is given on the rules of the National Sports Association on the treatment of asthma, which asthma medications are banned and how to apply for an exemption. Diagnostic studies for asthma are reviewed. In addition to spirometry before and after bronchodilatation, bronchial challenge tests and exercise tests are used. An overview of pathophysiology of swimmer's asthma is given and how it is connected to chloride that is used as a disinfectant. The incidence of asthma among competitive swimmers is reviewed.