Foy, H. M. (School of Public Health and Community Medicine, Univ. of Washington, Seattle, Wash. 98105), G. E. Kenny, R. McMahan, G. Kaiser, and J. T. Gray-ston. Mycoplatma pneumoniae in the community. Amer J Epidem 93: 55–67, 1971.— The epidemiology of Mycoplasma pneumoniae infections was studied by surveillance of 1) a suburban island of 16,500 residents, 2) three elementary schools, 3) university student groups, and 4) neighborhood households. M. pneumoniae pneumonia is endemic in Seattle. In 1966–1967, an epidemic occurred. Both during this epidemic period and in endemic years, attack rates varied considerably within the community as observed between different parts of the suburban island and between two similar elementary schools. The vectors of spread were usually children, who often suffered only mild illness. M. pneumoniae infection spread slowly but effectively between adjacent households with children playmates and through a sorority house, but not in two offices of employment. Transmission appears to occur primarily during acute disease. The carrier state, which lasted up to five months, did not give rise to secondary cases. Although most infected children had febrile lower respiratory tract disease, only 13% were diagnosed as having pneumonia. The endemic occurrence of M. pneumoniae infection in Seattle can be explained by slow spread from area to area, long incubation period and low communicability outside the family setting.