The Auckland District Health Board has issued an alert to doctors and other health professionals about a sharp jump in the number of cases of syphilis.
Health Ministry figures show the number has almost doubled in the Auckland region - from 44 in 2013 to 84 last year.
The board's acting chief medical officer Richard Sullivan said syphilis was very treatable, but awareness was needed.
"It's a combination of making sure the community is aware of the public health issue, of insuring that our health practitioners are in a position where by they are testing for it and treating it appropriately.
"And then it's understanding why - why we have gone to 44 for 84 and what other public health messages should we be giving to people who are at risk, who are at higher risk to reduce their risk of contracting syphilis."