Respiratory viral infections in adults cause significant morbidity and mortality, especially in high-risk patients. The impact of influenza virus, rhinoviruses, and respiratory syncytial virus in immunocompromised cancer patients and in asthma and chronic bronchitis patients has been documented in recent publications. Cytomegalovirus pneumonia continues to be a major cause of morbidity and mortality in transplant recipients. Newer rapid diagnostic tests and the use of polymerase chain reaction technology have provided better understanding of the causes and epidemiology of acute respiratory illness in adults. The approved neuraminidase inhibitors for influenzaviruses and the nonapproved capsid inhibitors of rhinoviruses may be useful in treating high-risk individuals. The inactivated influenza vaccine has been shown to benefit healthy adults and to be safe in asthmatic adults and children.