STI statistics in Australia: the 2025 numbers

In September 2026 the Kirby Institute released Australia’s latest sexual health surveillance data, covering the 2025 calendar year. The short version: chlamydia is still the most commonly notified STI, while syphilis and gonorrhoea diagnosis rates have both climbed more than 50% over the past decade. Below are the key numbers, what sits behind them, and what they mean if you’re sexually active in Australia.

The headline numbers (2025)

Chlamydia, gonorrhoea and syphilis are the three most commonly notified bacterial STIs in Australia. In 2025 there were 94,184 chlamydia, 42,393 gonorrhoea and 5,986 syphilis diagnoses. Chlamydia has fluctuated over the decade and eased slightly in the past year, while syphilis and gonorrhoea have both risen sharply — each up more than 50% in the diagnosis rate over ten years.

Chlamydia: still the most common

With 94,184 diagnoses in 2025, chlamydia is comfortably Australia’s most commonly reported STI. Around half of all diagnoses are in people aged 20 to 29. It often causes no symptoms, so many infections go undiagnosed — the only way to know is a chlamydia test. Rates among Aboriginal and Torres Strait Islander peoples are around 2.5 times those of non-Indigenous Australians. For the longer-term picture, see why chlamydia stays so common.

Gonorrhoea: up more than 50% over the decade

There were 42,393 gonorrhoea diagnoses in 2025. Men accounted for 73% of diagnoses, with higher rates among men who have sex with men, and rates around four times higher among Aboriginal and Torres Strait Islander peoples. Like chlamydia, gonorrhoea is often symptomless, so a gonorrhoea test is the only way to confirm it. Not sure which is which? See chlamydia vs gonorrhoea.

Syphilis: rising fastest in women

Syphilis reached 5,986 diagnoses in 2025, with the diagnosis rate up more than 50% over the decade. Most diagnoses are still among men (78%), but the steepest rise is among women — up 167% over ten years, compared with 39% among men. That matters most in pregnancy: untreated syphilis can pass to a baby (congenital syphilis). There were 14 congenital syphilis cases in 2025, and 40 infant deaths have been recorded over the past decade. National guidelines now recommend up to three syphilis tests during pregnancy. See syphilis testing and STI testing in pregnancy.

Who is most affected

Three patterns stand out in the 2025 data. Young adults carry much of the chlamydia burden — about half of diagnoses are in people aged 20 to 29. Men, particularly gay and bisexual men, make up the majority of gonorrhoea (73%) and syphilis (78%) diagnoses — though the fastest-growing group for syphilis is women. And Aboriginal and Torres Strait Islander peoples continue to experience substantially higher rates — roughly 2.5 times for chlamydia, four times for gonorrhoea and six times for syphilis — reflecting long-standing gaps in access to culturally safe care.

What’s working: prevention

There is good news in the data too. Among gay and bisexual men, syphilis and chlamydia diagnoses have fallen over the past three years — a decline researchers link to rising use of doxy-PEP (a single dose of doxycycline taken after sex to reduce the risk of bacterial STIs) alongside HIV PrEP. It’s a reminder that targeted prevention works. You can read more about what doxy-PEP is and broader STI prevention.

What this means for you

Most STIs have no symptoms, so testing is the only way to know — and it’s the single most effective thing you can do. A full screen covers chlamydia, gonorrhoea, syphilis, HIV and hepatitis B in one go. If you’re sexually active, a routine check is worthwhile, and it’s worth testing sooner after a new partner, condomless sex or any symptoms. With Clinic365 you can arrange it by phone with a Specialist GP and test at any pathology lab, Australia-wide — bulk-billed with Medicare.

Frequently asked questions

What is the most common STI in Australia?

Chlamydia, with 94,184 diagnoses in 2025 — far more than any other notifiable STI.

How many STI cases were there in Australia in 2025?

The three most commonly notified bacterial STIs recorded 94,184 chlamydia, 42,393 gonorrhoea and 5,986 syphilis diagnoses in 2025.

Are STIs rising in Australia?

Syphilis and gonorrhoea diagnosis rates are both up more than 50% over the past decade. Chlamydia has fluctuated and eased slightly in the past year, but remains the most common STI.

Which STI is rising fastest?

Syphilis — and fastest of all among women, up 167% over the decade compared with 39% among men.