In the 1950s and 1960s, following a decision by the Second World Health Assembly in 1949, mass treatment campaigns against the endemic treponematoses were undertaken with the support of the World Health Organization and the United Nations Children's Fund. The control policy was based on recognition of the importance (1) of screening at least 90% of the target population; (2) of conducting periodic resurveys and treating missed, new, and imported cases; (3) of treating the entire treponemal reservoir (including latent cases and contacts); and (4) of using adequate dosages of long-acting penicillin (minimal dosages were recommended). Later, policies on the extent of contact treatment at different levelsof endemicity were established. During these mass campaigns, ∼150 million clinical and latent cases and contacts were treated; prevalence of endemic treponematoses was reduced dramatically. The major reasons for resurgence of yaws and endemic syphilis in some areas are discussed. One important factor has been the failure of many countries to integrate active control measures into local health services after the mass campaigns. Yaws and pinta are continuing to decline to very low levels in the Americas. In West Africa, especially, incidence of yaws and endemic syphilis have returned to high levels. Fews ignificant endemic areas remain in Asia except in Indonesia and Papua New Guinea.