Campaigners in London are marking World Aids Day with an attempt to break an HIV testing record.
It comes as new figures suggested a record number of people in the UK - nearly 100,000 - are living with HIV.
People are being invited to have a 60-second test at the G-A-Y bar in London's Soho between 12pm and 8pm.
Last December's event at the venue officially broke a Guinness World Record for the number of HIV tests conducted in an eight-hour period.
A total of 467 tests were done and around £13,000 was raised for the Elton John Aids Foundation.
Staff from 56 Dean Street, Chelsea and Westminster Hospital's HIV and sexual health centre in Soho, are repeating the challenge to promote HIV awareness and "make history" again.
Jake Jenkins of 56 Dean Street said: "Come along to G-A-Y on World Aids Day to get a free instant and confidential HIV test and support our attempts to promote HIV awareness, reduce stigma and make history.
"The testing will be provided by the friendly, expert team from 56 Dean Street using the world's fastest antibody test which provides a result in just 60 seconds. Testing early can add, on average, 16 years to someone's life."
The PM wants more people to be educated about HIV and Aids The international annual campaign, symbolised with a red ribbon, is about increasing awareness of Aids, celebrating breakthroughs in treatment and remembering those who have died.
The Prime Minister has said too many people are not educated about HIV and Aids, and almost 25,000 people who have the human immunodeficiency virus are not aware they have been infected.
David Cameron said such people were not benefiting from treatment and were increasing the risk of passing on the virus.
He added: "This means up to 600 people a year could be dying from a preventable, treatable condition.
"People need to know that, diagnosed early, the outlook for most people with HIV in the UK today is a good one, thanks to the availability of effective treatment and the excellent care provided by the NHS.
"Above all, people need to know that it's never been quicker or simpler to get tested."
There were 6,280 people diagnosed with the virus last year, according to the Health Protection Agency.
Mr Cameron said World Aids Day should be used to "spread the message" about education, testing and early diagnosis.
HIV attacks the immune system and weakens the ability to fight infections and disease.
Aids is the final stage of HIV infection, when the body can no longer fight life-threatening infections.
HIV is found in the body fluids of an infected person, and about 95% of people are infected through sexual contact.
Snow and ice follow torrential rain and floods earlier in the week
Forecasters expect more snow this weekend
Health officials say all pregnant women should be vaccinated
Rwandan President Paul Kagame
The fighting has left thousands of people displaced
The winner is richer than Princes William and Harry - but may be unaware
The Weirs from Largs scooped the UK's biggest ever jackpot
The couple are visiting charities, schools and the city's famous university
Ms Dorries hears she is the first celebrity to be booted off (Pic: ITV)
The MP after her first bushtucker trial (Pic: ITV)
A family of three is rescued by the RNLI in Maisemore, Gloucestershire
Hotel owner Charlie Ryan and his dog are rescued in St Asaph
Firemen filled sandbags to deliver to residents in North Wales
Residents of St Asaph wade to safety
A resident collects her belongings in Willington, central England
Labour leader Ed Miliband has called the scheme a "miserable failure"
Sir Michael Wilshaw has criticised school standards in his report
The pub at the scene of the violence in Rome
A soldier carries a sandbag in Catterick, North Yorkshire
Residents load sandbags onto a trolley elsewhere in the town
A man rows through a car park in Keynsham, Somerset
A homeless woman died after being crushed by a tree in Exeter
A car is partially submerged in standing water in Ruishton, Somerset
Homes are left flooded on Cheats Road in Ruishton
Hay bales stand in flood water in fields surrounding the Glastonbury Tor
Flood water blocking the A361 near Taunton, Somerset
In Scotland, 443 stalkers have been successfully prosecuted since 2010
The site of a fallen tree in Exeter, where a 21-year-old woman died
Cars stranded in floodwaters outside homes in Malmesbury, Wiltshire
British team kayaker Sam Anderson takes to the water in Exeter
Flooding in Newlyn, Cornwall (Pic: Adam Gibbard)
The Prime Minister himself gave evidence to the inquiry
Lord Justice Leveson's report will be published on Thursday