The number of cases of syphilis have reached the highest level since 1949, new figures show.
Cases of the infection across England have rocketed since 2012, according to data from Public Health England (PHE).
In 2016, there were 5,920 syphilis diagnoses - an increase of 12% from the previous year (from 5,281 to 5,920) and a 97% rise from 2012 (from 3,001 to 5,920).
PHE said that the cases were mostly associated with transmission in gay, bisexual or other men who have sex with men.
Syphilis is a bacterial infection that's usually caught by having sex with someone who's infected.
It can usually be treated with a short course of antibiotics, but if left untreated can cause serious long term problems.
During 2016 there were 420,000 diagnoses of sexually transmitted infections (STIs) made in England, a decline of 4% compared to 2015, according to the PHE data.
It said the impact of STIs remains greatest in heterosexuals aged 15 to 24, black ethnic minorities and gay, bisexual and other men who have sex with men.
Commenting on the figures, Dr Michael Brady, medical director at sexual health charity the Terrence Higgins Trust, said: "Today's figures show unacceptably high rates of STIs.
"We're facing huge challenges, such as the continued rise of syphilis and ongoing concerns around drug-resistant gonorrhoea, and we urgently need to address the nation's poor sexual health and rates of STIs in those most at risk.
"In this climate of cuts to local authorities' public health budgets, this is particularly concerning. Now is not the time to be scaling back sexual health services.
"Cuts to chlamydia testing, for example, are having a visible impact, with today's figures showing that there has been a 9% decrease in the number of chlamydia tests taken.
"It is also now essential that Public Health England, the Department of Health and local authorities ensure improved access to effective STI and HIV testing, treatment and prevention services.
"Otherwise, we cannot expect to address the ongoing sexual health crisis."