Auckland is being touted as the 'City of Syphilis' in a new report.

The New Zealand Medical Journal report reveals the number of cases managed at the Auckland Regional Central Health Service has steadily increased.

In 2015 it recorded the largest number of cases reported ever with 152 cases managed at their service.

This was a 78 per cent increase on the 84 Auckland cases the year before.

Author Sunita Azariah said even that number is under-estimated because clinics don't have to notify authorities of a diagnosis.

"Syphilis is not a notifiable condition at the moment so the only cases that get reported are from public sexual health clinics. Other health services manage it but it's not reported."

But she said from January next year it will be a notifiable disease.

Ms Azariah said at the start of her career syphilis was almost non-existent, now 20 years later it's something she sees often.

But she said it's a complex condition that can be difficult to diagnose - up to half of cases don't have any symptoms.

"We tend to recommend if it's a doctor who's not familiar with managing syphilis that they refer them or discuss them with the local sexual health service, because there are issues that need to be gone into like contact tracing and follow up."