For 30 years, chancroid has been an uncommon and geographically localized disease in the United States; a mean of 878 cases were reported annually between 1971 and 1980. Since 1981, however, numerous outbreaks have established chancroid as an endemic disease in many additional areas and, in 1986, 3418 cases, the largest number since 1952, were reported. Cases are occurring preponderantly among men who patronize prostitutes, and infected individuals who have traveled from outbreak areas or from outside the United States are suspected of having contributed to the spread of disease. Efforts to eradicate disease in outbreak areas have been only occasionally effective and have been hampered by difficulty in locating potentially infected individuals and by travel by infected individuals. The failure to eradicate outbreaks leaves residual sources for new disease transmission into yet additional areas.