All 171 patients admitted to four study rooms containing cribs were under surveillance during the winter and spring for development of nosocomial respiratory and infection. One sixth of the 90 children at risk acquired respiratory illness while in the hospital. Viruses were isolated from two thirds of the patients with nosocomial infections: rhinovirus, respiratory syncytial virus, parainfluenza, and influenza A and B. Serial viral cultures of the children under surveillance suggested that nine of 11 virus-positive nosocomial infections were not acquired from a roommate. Furthermore, the risk to a patient of becoming infected with a virus being shed by a roommate was only 3%. The need for isolation of all children with respiratory illness in a single room with a separate air exhaust system is not suggested by these data.