Syphilis is a sexually transmitted infection (STI) caused by the bacterium Treponema pallidum and has shown a significant increase in recent decades. It may be associated with other STIs such as soft chancre or chancroid, which is an uncommon infection in Brazil. The presence of ulcerated genital lesions is associated with a higher risk of HIV transmission. An accurate clinical and laboratory diagnosis of genital ulcer disease is essential for the appropriate treatment of pregnant women, in order to avoid congenital syphilis, a severe complication of mother-to-child vertical transmission. We report the case of a woman in the third trimester of pregnancy with Rollet's mixed chancre and describe the clinical and laboratory diagnosis, as well as the treatment of these diseases in pregnancy. We emphasize the importance of training health professionals on early diagnosis and treatment in order to avoid mother-to-child transmission.