A new report card on Australia's sexual health is a mixed bag, with HIV infections stable but gonorrhoea and syphilis on the rise.

The number of Australians contracting HIV has stabilised but about a thousand people a year are still returning positive tests.

And about a quarter of those people have had the virus for at least four years without realising it.

The latest report card on the nation's sexual health, by the University of NSW's Kirby Institute, is a mixed bag.

While new HIV infections have flattened out over the past three years, along with chlamydia in recent times, more Australians are being diagnosed with gonorrhoea and syphilis.

And rates of sexually transmitted infections remain much higher in Australia's indigenous population, with the HIV diagnosis rate increasing over the past five years.

Experts say Australia is close to achieving the UN's HIV targets to ensure 90 per cent of all people living with the virus know their HIV status by 2020 and are being treated to ease its effects and suppress transmission.

But they say Australia still has more to do to identify and treat infections early.

"Over a quarter of the people diagnosed with HIV in Australia last year already had substantial damage to their immune systems," says Kirby Institute Associate Professor Rebecca Guy.

"That indicates they likely contracted their infection a number of years ago.

"Every year that a person delays being diagnosed is a year that they miss out on treatment to help maintain healthy immune function, and a year that they are at higher risk of passing on the virus to their sexual partners."

Professor John de Wit, from UNSW's Centre for Social Research in Health, says there's evidence of a gradual increase in the number of gay men who don't insist on condoms for anal sex with casual partners.

But he says they are increasingly looking to other forms of infection prevention, including new technologies such as pre-exposure prophylaxis, or PrEP, a pill taken daily by people who don't have HIV but are at risk of contracting it.

When taken consistently, PrEP has been shown to reduce the risk of HIV infection in people who are at high risk by up to 92 per cent.

"It should also be noted that two thirds of men at high risk of HIV infection are testing two or more times per year, and that's a really important development," he says.

Experts say the rise in gonorrhoea and syphilis infections is concerning but could be the result of more widespread testing, rather than an actual spike in infections.

Chlamydia remains the most frequently reported sexually transmitted disease in Australia with 86,000 cases diagnosed in 2014, most among 15 to 29-year-olds.

However diagnosis rates have been relatively stable for the past few years, and infections among the youngest Australians, aged 15 to 19, are falling.

A record 1999 cases of syphilis were reported in 2014, and sexual health experts say that's unacceptably high.

But despite the record figure, syphilis remains a relatively uncommon infection in Australia and it's estimated to be nothing like the levels seen in the pre-AIDS era when testing for the disease was less common.

The report shows a drop in new cases of hepatitis B, probably as a result of Australia's immunisation programs.

But deaths related to chronic hepatitis C have increased by a staggering 146 per cent in a decade - from 280 in 2004, to 690 last year - as people infected decades ago age and fail to get treatment.

"This all stands to change if we see approval of funding for breakthrough new treatments that have the potential to turn around Australia's hepatitis C epidemic," the Kirby Institute's Professor Greg Dore says.