Respiratory Syncytial Virus (RSV) is the leading cause of hospitalization for lower respiratory tract infections (LRTI) in young children worldwide. RSV is an important cause of LRTI in infants and a variety of factors, such as gender, age at admission, gestational age, birth weight, and exposure to tobacco smoke and breast feeding may affect the prevalence of RSV-related disease and, possibly, the risk of developing asthma-like symptoms during the school years. AAP in 2006 formulated the new guidelines on diagnosis and management of bronchiolitis, giving recommendations on different conditions requesting clinical decisions also in terms of prevention.