Approximately 14,600 cases of respiratory illness in 4,905 residents of Tecumseh, Mich, were studied during a six-year period. The annual incidence of respiratory illness for each individual was calculated. Rates decreased with age except during the 20- to 29-year decade. In children less than 3 years of age, males experienced more illnesses than females; in those older than that, the reverse was true. Frequency of physician consultation varied with illness type. Rhinoviruses were the most frequently isolated pathogen from all illnesses. From those associated with physician consultation, group A hemolytic streptococci were nearly as frequently isolated. More illnesses started on Monday than on any other day of the week. Illness frequency increased with education of head of household, but decreased with family income. Therefore, highest rates were observed in more educated families with low income.