After many years the incidence of infective syphilis (infection with Treponema pallidum) is increasing in the United Kingdom. This may reflect changes in sexual attitudes and behaviour, altering trends in HIV disease, and increased foreign travel. Oral disease as a consequence of primary syphilis is rare. The present report details two patients presenting to an oral medicine clinic in London, within a 6-month period in 1999, with oral ulceration as their only clinical manifestation of undiagnosed primary syphilis. The oral aspects of early syphilis and the need for dentists to be aware of changing epidemiological trends in relevant infectious diseases are highlighted.