Among industrialized nations, the rate of rehospitalization in the United States for respiratory syncytial virus (RSV) is approximately 30 per 1000, exceptions being noted for American Indians and Alaskan natives, two ethnic groups who tend toward higher rates of RSV hospitalization. In distinction Japan reports an admission rate of 60 per 1000 for RSV disease. Yet Japan ranks considerably lower than many of its western counterparts in premature births. Whether an RSV subtype, a new viral genotype or some other unifying characteristic exists that might explain the severity of adenovirus, parainfluenza and RSV infections in this region of Asia remains to be determined. Outcomes trials in the United States, Canada, United Kingdom, Denmark and Japan all identified crowding and exposure to tobacco smoke as significant and independent risk factors for disease severity of RSV. The epidemiology of RSV is largely consistent throughout Europe, with peak outbreaks occurring in December and January. In Europe RSV accounts for 42 to 45% of hospital admissions for lower respiratory tract infections in children younger than 2 years of age, and inpatient populations tend to be younger and to experience greater disease severity. For RSV bronchiolitis lengths of stay in European hospitals range from a low of 4 days to a high of 10 days.The Infección Respiratoria Infantil por Virus Respiratorio Sincitial Study Group in Spain conducted 2 prospective observational studies in 14 and 26 neonatal units, respectively, on nonprophylaxed neonates to determine hospitalization rates for respiratory syncytial viral illness during 2 consecutive RSV seasons. Throughout each respiratory season the study group followed premature infants of