The epidemic caused by the new Asian strain of type A influenza virus in the United States was preceded by a series of localized outbreaks during the summer of 1957. The epidemic, which was explosive in character in the fall, was succeeded by a series of localized outbreaks in the first 3 months of 1958. Mortality was approximately the same as in epidemics during the preceding decade which were caused by A-prime strains of virus. Deaths were most common in the older age groups. The largest increase in mortality was in the cardiovascular diseases. Influenza and pneumonia accounted for only about one-quarter of the excess mortality during the epidemic.