The respiratory syncytial virus is the most common cause of infection of the lower respiratory tract in infants and young children, and is the leading cause of hospitalisation and death due to viral illness during the first year of life. In otherwise healthy infants, the virus usually causes only mild respiratory illness, but premature babies and infants with chronic lung disease, those with congenitally malformed hearts, or those who are immunodeficient, are at increased risk of serious illness, hospitalisation, and death. Recent infection with the virus is also associated with increased postoperative complications after corrective surgery for congenitally malformed hearts. No effective vaccine is currently available, and treatment is limited to supportive therapy. Prevention in groups deemed to be at high-risk, therefore, is essential. In addition to measures for control of infection, prophylactic immunotherapy is indicated in selected patients. Palivizumab (Synagis®) is a monoclonal antibody indicated for the prevention of serious viral disease of the lower respiratory tract in premature infants, those with chronic lung disease, and those with haemodynamically significant congenital cardiac lesions. Palivizumab is given intramuscularly, usually as a monthly injection during the so-called “season”. In a recent international, randomised, double-blind, placebo-controlled trial in 1,287 children less than or equal to 2 years old with haemodynamically significant congenital cardiac malformations, prophylaxis achieved a relative reduction of 45 per cent in the incidence of antigen-confirmed viral-related hospitalisation, and reduced the duration of hospital stay by 56 per cent. National and international guidelines, therefore, now recommend routine prophylaxis in the first year of life in children with haemodynamically significant congenital cardiac disease.