Gonorrhoea and syphilis that belong to our oldest recognized sexually transmitted diseases (STD) are also the prototypes of curable STDs. After the discovery of the causative organisms, Neisseria gonorrhoeae in 1879 and Treponema pallidum in 1905, diagnostic tests were developed and by this, in conjunction with instituted regulations and legislation, means were created for public health authorities to collect statistical data. Sweden has fairly reliable statistics of both syphilis and gonorrhoea from 1912 and onwards, and these data show many interesting characteristics. Syphilis was prevalent in Sweden among both males and females during World War (WW) I and peaked in 1920 with an incidence rate of 150 and 75 per 100,000 population, respectively. The incidence figures fell rapidly after 1920 and reached a low of less than 30 cases per 100,000 in the mid 1920s, probably as a result of systemic treatment with Salvarsan in conjunction with vigorous contact tracing, two important measures to bring an infectious disease under epidemiological control. There was a slight increase of male syphilis in the late 1920s and early 1930s, and of both male and female cases during WW II which never reached the incidence figures of WW I. Penicillin was introduced in the mid 1940s for treatment and was proved superior to Salvarsan. The incidence figures have been very low ever since the early 1950s.(ABSTRACT TRUNCATED AT 250 WORDS)