ALTHOUGH there is debate about its geographic origin, syphilis has been clearly described since the 15th century, as has its sexual mode of transmission.1 In the early 20th century, syphilis was a leading cause of neurologic and cardiovascular disease and a major public health problem.2 Even before the introduction of penicillin, the combination of effective therapy and organized public health measures caused syphilis rates in the United States to decline, and by the mid-1950s the disease was relatively uncommon. Between 1955 and 1985, relatively few cases of syphilis were diagnosed (Fig. 1); as a result, many clinicians are now unfamiliar. © 1992, Massachusetts Medical Society. All rights reserved.