Big Brother 2004, also known as Big Brother 4, was the fourth season of the Australian reality television series Big Brother, and was aired on Network Ten, starting on Sunday 2 May 2004, with the housemates entering the day before, and ended on Monday 26 July 2004, lasting 86 days. The season was billed as "back to basics, but with one small secret". In a return to the basic format of Big Brother 1 and Big Brother 2 that had been eschewed in favour of twists and surprises in Big Brother 3, all housemates were let into the house together and former surprise elements such as swimming pools and gym equipment were all exposed from the beginning.