Horwitz, Ole (Danish Tuberculosis Index, 25 Svanemøllevej, Copenhagen Ø, Denmark). Long-range evaluation of a mass screening program. Am J Epidemiol 100: 20–28, 1974.—In 1950–1952 a mass screening program for tuberculosis was carried out in Denmark. All young adults between 15 and 34 years of age were invited to participate; of these, 463,099 (63%) attended while 266,703 (37%) did not. Among the participants, 4973 died from all causes during a 12-year follow-up period; among the non-participants 3802 died; the death rate per 100,000 was 90 and 119 per 100,000, respectively. Based on the number of deaths from tuberculosis among the participants and the non-participants, it is estimated that the mass campaign prevented a maximum of 50 TB deaths. The effect of the campaign can then be illustrated by the following figures: The expected number of TB deaths among the participants was reduced by 67%; among all invited (participants + non-participants) it was reduced by 37%. The prevented deaths from TB meant that the total death rate (all causes) was reduced by 1% among the participants, and by a scant 1% among the target population (participants + non-participants). Related to all TB deaths occurring in all Denmark in the same period, the prevention of 50 fatal cases involved a 2% effect. When the 50 prevented deaths are related to all deaths from all causes, the effect approaches zero per cent.