Key points: - In 2001, a surveillance system was established at participating sites, and trends in Extencilline® sales at private pharmacies were analyzed. - The number of syphilis cases doubled from 2001 to 2002, followed by relative stability in 2003. The Île-de-France region is the most affected. - Increase in Extencilline® sales across all regions, particularly in Île-de-France. - Homosexuals are the most affected population, half of whom are HIV-positive. - Persistent transmission of syphilis in 2003, partly due to the continuation of risky behaviors, particularly unprotected oral sex. (R.A.)