IFK Göteborg won the league ahead of runners-up IFK Norrköping, while IK Brage, Örgryte IS and Hammarby IF were relegated.
The league was contested by 12 teams, with IFK Göteborg winning the league and the Swedish championship after the play-offs.
The 1990 Allsvenskan play-offs was the ninth and final edition of the competition.
The four best placed teams from Allsvenskan qualified to the competition.
Allsvenskan champions IFK Göteborg won the competition and the Swedish championship after defeating IFK Norrköping who finished as runners-up in the league.