Four isolated cases of congenital syphilis born to mothers who screened syphilis negative in the first trimester were identified between March 2016 and January 2017 compared with three cases between 2010 and 2015. The mothers were United Kingdom-born and had no syphilis risk factors. Cases occurred in areas with recent increases in sexually-transmitted syphilis among women and men who have sex with men, some behaviourally bisexual, which may have facilitated bridging between sexual networks.