During the 1987 through 1988 seasonal peak of respiratory syncytial virus (RSV), 177 courses of ribavirin were administered at St Christopher's Hospital for Children, a tertiary care medical center in Philadelphia, Pa. Charts were reviewed on 100 treated patients with proved or suspected RSV disease to determine adherence to American Academy of Pediatrics treatment guidelines. Ninety-four percent fulfilled criteria for the risk of significant morbidity: cardiac, pulmonary, or immunodeficiency conditions (38%); an age of 6 weeks or younger (35%); or severe illness (21%). Severe illness was defined as hypoxemia, hypercapnia, or marked tachypnea. Of those treated because of underlying conditions, 71% had RSV documented, as did 71% of patients aged 6 weeks or younger and 81% of patients with severe disease. A study of 80 consecutive patients who were hospitalized with illness compatible with RSV infection revealed that 56% of patients were treated with ribavirin. Adherence to guidelines led to ribavirin use in half of the hospitalized patients with suspected RSV infection. The majority of these patients received therapy because of underlying conditions or very young age.