Yaws was introduced into the Americas by African slaves beginning in the 16th century and may have already been present before the arrival of Columbus. In the 1950s, programs for the eradication of yaws were undertaken in almost all American countries in which yaws was endemic. By mass treatment of cases and contacts with penicillin, the programs against yaws have dramatically reduced the incidence of reported cases throughout the Western Hemisphere from greater than 44,000 cases per year during 1950-1954 to 437 cases in 1975. In Brazil, efforts against yaws reduced the number of patients treated by 99% between 1965 and 1974. By 1975, yaws apparently remained a significant public health problem in only a few communities in Brazil, Columbia, Dominica, Ecuador, Haiti, Peru, St. Lucia, and St. Vincent, and possibly in Guiana and Surinam. It may be possible to eliminate infectious yaws entirely from the Western Hemisphere within the next few years.