High levels of syphilis in Canterbury are being blamed, in part, on dating apps.
The Institute of Environmental Science and Research said the number of infectious syphilis cases reported by Sexual Health Clinics increased from 82 in 2013, to 140 cases last year.
The highest numbers were recorded in the Auckland and Canterbury regions.
Canterbury Medical Officer of Health Ramon Pink said the increase was partly due to dating apps leading to a rise in unprotected sexual encounters.
He said Cantabrians who had unprotected sex, or who had multiple sex partners, should get a sexual health check for Christmas.
If left untreated, syphilis can cause damage to nerves, bones, skin, eyes and the brain.