Recent trends in western Europe show an increase in sexually transmitted infections (STIs). Available surveillance data in Switzerland confirm this rising trend. Gonorrhoea rates more than doubled between 1996 and 2003, and for Chlamydia there was a 64% increase from 1999 to 2003. Notifications of syphilis cases almost doubled in the year 2002 and rose to 174% compared to the period of 1998-2001. The resurgence of syphilis in 2002 and 2003 was most important in Zurich and Geneva with 54 and 24% of all cases, respectively. Eighty-four percent occurred in males, 40% affecting males who had sex with males, and at least 17% were HIV co-infected. For 2004, further increases in these bacterial STIs are expected. Increased awareness of the symptoms and signs of acute infections is needed as well as considering the diagnosis of STIs in patients with vague symptoms. In addition, laboratory reporting or mandatory disease notifications are needed to monitor syphilis trends in Switzerland.