The 1990–91 Primeira Divisão was the 57th edition of top flight of Portuguese football. It started on 19 August 1990 with a match between Farense and Nacional, and ended on 26 May 1991. The league was contested by 20 clubs with Porto as the defending champions.
The other two teams were replaced by Salgueiros, Gil Vicente, Farense and Famalicão from the Liga de Honra, as the league increase from 18 to 20 teams.