Respiratory viral infections are very important triggers of asthma exacerbation. Recent epidemiologic studies support the hypothesis that they are associated with 80 to 85% of acute attacks of asthma in children. The respiratory syncytial and parainfluenza viruses are predominantly detected in infants, while rhinovirus and mycoplasma are the commonest in children. In practice for an asthmatic child, it is necessary: 1. to vaccinate against influenza; 2. resume or increase the inhaled antiinflammatory therapeutics in moderate to severe asthma, before the viral epidemic season; 3. teach the child and his family on the attitude to have during an upper respiratory infection and when to visit a physician.