The 1991 1. divisjon, Norway's second-tier football league, began play on 28 April 1991 and ended on 6 October 1991.
The league was contested by 24 teams, divided in two groups and the winner of each group won promotion to Tippeligaen, while the runners-up played a promotion-playoff against the 10th placed team in the 1991 Tippeligaen.
The bottom three teams were relegated to the 2. divisjon.
Mjøndalen and Ham-Kam won promotion to Tippeligaen, while Kristiansund, Frigg, Surnadal, Mjølner, Råde and Sandefjord was relegated to the 2. divisjon.
Brann won the qualification round[1] and was promoted to the 1992 Tippeligaen.