In scuba diving, the density of the gases supplied increases with depth. During ascent, overinflation of the lungs is avoided by exhalation. In case of airway obstruction, the theoretical risk of pulmonary barotrauma and drowning increases. For this reason, asthma has been considered as a contraindication to scuba diving. This recommendation is often ignored and many people with asthma dive, apparently without problems. Certifying that an asthmatic patient is fit to dive remains a controversial and difficult matter. In case of mild intermittent asthma, scuba diving seems possible when the pulmonary function test is normal and the patient is asymptomatic, including during exercise and exposure to cold air. The asthmatic diver should be fully informed of the risks incurred and should notify his or her informed-consent to the physician.