Horwitz, O. (Danish Institute of Clinical Epidemiology, 25 Svanemøllevej, 2100 Copenhagen, Denmark), K. Grünfeld, B. Lysgaard-Hansen and K. Kjeldsen. The epidemiology and natural history of measles in Denmark. Am J Epidemiol 100: 136–149, 1974.—From the national (central) population register for Denmark, a random sample of all children aged 0–14 years was drawn. A questionnaire was sent for each sampled child (a total of 6804 individuals); 6333 (93%) replied. According to the given information, 6126 children could be classified according to their measles (rubeola, morbilli) history; 207 could not be classified and were excluded from the analysis. Among the 6126 children, 612 contracted measles in 1972. The incidence among susceptible children (who had not previously had measles) increased from 100 per 1000 among the youngest to a peak 500 per 1000 among the 6-year-olds; thereafter the rate declined. The incidence was similar in urban areas and rural districts and among girls and boys up to 6 years of age. Girls older than 6 years had higher rates. The clinical course was explored through an interview by a specially trained public health nurse. Four hundred children who had measles in 1972 were selected; all but 13 were interviewed. The diagnosis was confirmed in 382 of the interviewed cases. The disease ran an uncomplicated course in 82%, while 18% of the children had one or two complications. Most frequent were infections of the respiratory system (7%), otitis media (9%) and other inflammatory conditions (3%); one child had encephalitis. The parents judged the course as severe in 28%, as medium in 46%, and as mild in 27%. Nearly half (45%) of the parents who were gainfully occupied outside the home were absent from work in order to care for the children; on the average, a case of measles means the loss of 1.3 man-days. Among the parents, 54% had positive attitudes towards measles vaccination, 30% were negative and 16% were undecided. The results of the sample were converted to a nationwide scale. Estimates are given of the annual number of cases (with or without complications), the number of requested medical visits, as well as the number of children who submitted to chemotherapy or were admitted to hospital.