Viral infections of the respiratory tract are certainly the most common cause of infectious illness in most countries. People in all age groups are susceptible, but for those at the extremes of life these illnesses are particularly hazardous. Viral respiratory infections are more common in children under the age of five years, but in the first year of life, they are more severe. In the elderly, degenerative processes of the heart or lungs make pneumonia a more frequent and serious complication, and the same is true for patients of all ages suffering from chronic cardiac disease or chronic bronchitis. On the whole, the vast majority of viral respiratory infections are mild though often uncomfortable conditions, but sometimes the illness is severe and constitutes a threat to life. Unfortunately, there is no method whereby the spread of infection can be prevented. Adequate ventilation and avoidance of crowds are clearly advisable.