The High Court has told the NHS in England it can fund a drug that can prevent HIV - after health bosses argued it was not their responsibility.
NHS England previously said councils should provide the pre-exposure prophylaxis (Prep) drug as they are in charge of preventative health.
This stance was successfully challenged by the National Aids Trust (NAT).
But the High Court ruling does not make funding of Prep automatic and the NHS is set to appeal.
The ruling by Mr Justice Green said health bosses had "erred" in arguing it was not their responsibility.
NHS England has already announced it will appeal against the ruling - and even if that goes against health bosses it is not a given that Prep will be considered effective enough to warrant NHS funding.
If the Court of Appeal uphold the ruling NHS bosses would then assess Prep's cost-effectiveness alongside the merits of other treatments the NHS is being asked to provide.
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Using Prep has been shown to reduce the risk of HIV infection by 86%.
The once-a-day pill, which costs £400 a month per person, works by disabling the virus to stop it multiplying.
It is currently used in the US, Canada, Australia and France to help protect the most at-risk gay men.
Harry Dodd, 25, is one of about 500 homosexual men in England who are taking Prep as part of a trial called Proud.
He says: "I've seen the panic on the face of previous boyfriends when they are awaiting their [HIV test] results - it's a huge fear and it affects everything you do.
"To be able to have sex without having that fear hanging over you all the time is huge."
Harry says taking Prep has still not become socially acceptable.
"Too many people seem to think it will encourage a hedonistic lifestyle, but for me this is about saving lives," he says.
"People reacted with cynicism when the contraceptive pill for women was first introduced.
"For me, taking Prep has helped me to trust again, have relationships and build bridges and that shouldn't be taken away."
NHS England had argued that because Prep was preventative it was not its responsibility.