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Syphilis - an old imitator is back on the stage Syphilis is one of the oldest sexually transmitted infections and caused by the spirochete Treponema pallidum. The incubation time is 10-90 days and patients are contagious for approximately one year. In Sweden all blood donors and pregnant women are screened. By law, individuals with early syphilis (primary and secondary stages) are reported and contact tracing is performed. The syphilis incidence is increasing in Europe, USA and many other countries. The main drivers are men having sex with men. Diagnosing syphilis can be challenging because the non-tender, often genital ulcer of primary syphilis can go unnoticed.  Symptoms during secondary syphilis can be flu-like such as fever, lymphadenopathy and headache; an unspecific skin rash can appear. Serologic tests are usually positive 1-2 weeks after infection. Treatment of choice is benzathinpenicilllin 2.4 million units intramuscularly. Four case reports illustrate the diverse scenario of syphilis infection.