Big Brother 2009 was the fifth series of the Finnish version of the reality show Big Brother. The show aired from August 26, 2009 to November 29, 2009, lasting 97 days. For the fifth series, the house has been split into two sides with one side representing 'Paradise' and the other representing the 'Slums'. The concept of Head of House was introduced into this series.
Vappu Pimiä was the host of the Big Brother Talk Show and Jani Toivola hosted Big Brother Extra. This was the last series where Pimiä served as a hostess; the fifth season was the only series in which Toivola appeared.
The open auditions for the series were completed in April 2009.
Fourteen housemates entered the House at Launch. Justiina entered on Day 18, and Toni and Marko entered on Day 27, after the eviction of Lotta and Tuija. The final four housemates - Antti, Iida, Saranna and Stephania - entered on Day 55, after Minna's eviction.
^[I] Contestant's age at the start of the season.
It was announced during the show, that another Big Brother Swap would take place, this time with the third regular season of the Philippine franchise of Big Brother, dubbed Pinoy Big Brother. This would also be the second time that Big Brother Finland linked up with other foreign versions of the show, Season 4 being the first, when housemate Johan Grahn traded places with Munyaradzi Chidzonga from the third season of Big Brother Africa. The Philippine version boasts of being the first Big Brother franchise with two separate and complete houses, which compete each week for their weekly budget. On Day 66, Kätlin Laas left the Big Brother house. The following day, it was announced that Catherine "Cathy" Remperas, a 22-year-old registered nurse from Bohol, Philippines would be swapped with Kätlin. Kätlin left the Big Brother Finland House on Day 66 (Day 26 of the Philippine version) and enter either Philippine House on Day 69 (Day 29 of the Philippine version). She was supposed to arrive in the Philippines and enter either House the day before, but her flight was delayed due to weather disturbances caused by Typhoon Mirinae. Hours before her entrance, she had a brief appearance on the show The Buzz. On the other hand, Cathy was supposed to leave in the morning of Day 68 (Day 28 of the Philippines version) but their flight was postponed to a later hour of the day.