 Management is generally supportive, whereas symptom reducing therapy is debated with no international consensus. Furthermore, there are many unresolved questions related to the prognosis of bronchiolitis, its role in development of chronic lung disease in particular regarding the association between early bronchiolitis and asthma development. The present project will particularly focus on: 1Treatment efficacy related to various outcomes during active disease, 2 retrospectively assess treatment efficacy in relation to later development of allergic disease, 3 assess the role between different vira and asthma prognosis as well as 4 identify possible prognostic factors involved in the progression from bronchiolitis to further airways disease. 