The 2005 1. divisjon (referred to as Adeccoligaen for sponsorship reasons) was a Norwegian second-tier football season.
The season kicked off on 10 April 2005, and the final round was played on 30 October 2005.
Sandefjord will be playing in the top division for the first time while Stabæk return to Tippeligaen after being relegated in 2004.
Mandalskameratene, Skeid, Tønsberg and Alta were relegated to the 2006 2. divisjon at the end of the season.
They were replaced by 2004 2. divisjon winners Tønsberg, Follo, Løv-Ham and Alta.