McGowan, John E., Jr., J. A. Bryan and M. B. Gregg (Viral Diseases Branch, Epidemiology Program, CDC, Atlanta, Ga. 30333). Surveillance of arboviral encephalitis in the United States, 1955–1971. Am J Epidemiol 97: 199–207, 1973.—Since 1955, the Center for Disease Control has conducted nationwide surveillance on the occurrence in the United States of encephalitis due to arboviruses. In the first 17 years of this program, 1955–1971, there were 3739 reported cases of encephalitis associated with arboviral infection, with 260 deaths. The arboviruses most frequently associated with these cases were St. Louis encephalitis (2349 cases), Western equine encephalomyelitis (762 cases), California encephalitis (504 cases), Eastern equine encephalomyelitis (116 cases), and Venezuelan equine encephalomyelitis (6 cases). For most of the past 17 years, St. Louis encephalitis virus was the most commonly reported arbovirus, and marked geographic differences in age-specific attack rates were noted for cases associated with this virus. A number of epidemiologic features vary for the different viruses and can point to probable etiology. Recognition of these features may be of help in making estimates of prognosis.