Big Brother 2004, also known as Big Brother 5, was the fifth series of the British reality television series Big Brother, which premiered on Channel 4 on 28 May 2004 and lasted 71 days until the live finale on 6 August 2004.
Following the poor reception and ratings for Big Brother 4, producers decided to cast a more controversial set of housemates and introduced an 'evil' Big Brother. This saw an increase in ratings when compared to the previous edition. In total, the series averaged 5.1 million viewers, thus making it the second highest rated so far, only behind Big Brother 3.
The premise of the series remained largely unchanged from the previous instalment in the series, in which a certain number of strangers lived in a house together with no communication with the outside world, filmed constantly during their time in the house, trying to stay in the house for as long as possible in hopes of being voted the winner by the viewing public. It was the first series to feature a prize fund of up to £100,000. Certain elements of the show which had been present since Big Brother's inception in 2000 were removed, such as the hot water only being present for one hour in the morning, the vegetable patch and the chickens.
A number of controversies hit the fifth series of the show; it was the first summer series to feature sex between housemates – although the previous Teen Big Brother: The Experiment special edition series in 2003 was the first overall. The fifth series is also notorious for the infamous 'Fight Night', when on Day 20, police entered the house after being called by viewers to stop a mass brawl in the house. The first two housemates to leave the house were removed due to unacceptable behaviour, making it the first time since the first series to feature housemates being disqualified for breaking the rules.
For the first time ever, housemates were selected through an open audition process and a total of 13 housemates featured; the series lasted 71 days, in which housemate Nadia Almada was crowned the winner during the live series finale.
Since their appearance on Big Brother 5, numerous housemates have gone on to appear in later editions of the programme. Housemates Kitten, Marco, and Victor all appeared on the spin-off series Big Brother Panto in 2004, along with housemates from the previous four editions. Housemate Michelle later appeared on Big Brother 10 to participate in a task celebrating ten years of the programme. Housemates Nadia, Michelle, and Victor were all official housemates on Ultimate Big Brother in 2010, with Nadia and Michelle being the third and fourth evicted housemates, respectively. Victor made it to the finale of the season, where he came in fourth place. Housemates Ahmed and Marco both made appearances in that series, though they were not competing to win.