| Competition: | Primeira Divisão |
| Season: | 1990–91 |
| Winners: | Benfica 29th title |
| Relegated: | Tirsense Vitória de Setúbal Estrela da Amadora Belenenses Nacional |
| Continentalcup1: | European Cup |
| Continentalcup1 Qualifiers: | Benfica (first round) |
| Continentalcup2: | Cup Winners' Cup |
| Continentalcup2 Qualifiers: | Porto (first round) |
| Continentalcup3: | UEFA Cup |
| Continentalcup3 Qualifiers: | Sporting CP (first round) Boavista (first round) Salgueiros (first round) |
| League Topscorer: | Rui Águas (25 goals) |
| Biggest Home Win: | Chaves 6–0 Beira-Mar (28 April 1991) |
| Biggest Away Win: | Penafiel 2–5 Sporting CP (26 August 1990) |
| Highest Scoring: | Tirsense 4–4 Boavista (12 January 1991) Braga 6–2 Nacional (2 February 1991) |
| Matches: | 342 |
| Total Goals: | 874 |
| Prevseason: | 1989–90 |
| Nextseason: | 1991–92 |
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.
Benfica qualified for the 1991–92 European Cup first round, Porto qualified for the 1991–92 European Cup Winners' Cup first round, and Sporting CP, Boavista and Salgueiros qualified for the 1991–92 UEFA Cup first round; in opposite, Tirsense, Vitória de Setúbal, Estrela da Amadora, Belenenses and Nacional were relegated to the Liga de Honra. Rui Águas was the top scorer with 25 goals.
Portimonense and Feirense were consigned to the Liga de Honra following their final classification in 1989-90 season.
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.
| Team | Outgoing manager | Date of vacancy | Position in table | Incoming manager | Date of appointment | |
|---|---|---|---|---|---|---|
| Vitória de Guimarães |  Paulo Autuori | 23 September 1990 | 13th |  Pedro Rocha | 24 September 1990 | |
| Marítimo | 23 September 1990 | 17th | Paulo Autuori | 24 September 1990 | ||
| Penafiel | 30 September 1990 | 20th |  Vítor Manuel | 1 October 1990 | ||
| Braga | Raul Águas | 28 October 1990 | 19th | Carlos Garcia | 29 October 1990 | |
| Belenenses |  Henri Depireux | 21 October 1990 | 19th | Antônio Lopes | 1 November 1990 | |
| Boavista | João Alves | 14 November 1990 | 5th | Raul Águas | 9 December 1990 | |
| Vitória de Setúbal | José Romão | 2 December 1990 | 19th | Quinito | 3 December 1990 | |
| Chaves | Manuel Barbosa | 23 December 1990 | 18th | José Romão | 24 December 1990 | |
| Belenenses | Antônio Lopes | 6 January 1991 | 18th | Moisés Andrade | 7 January 1991 | |
| Vitória de Guimarães | Pedro Rocha | 12 January 1991 | 12th | João Alves | 13 January 1991 | |
| Estrela da Amadora | Manuel Fernandes | 27 January 1991 | 15th | Jesualdo Ferreira | 28 January 1991 | |
| Nacional | Jair Picerni | 2 February 1991 | 17th | Manuel de Oliveira | 3 February 1991 | |
| Nacional | Manuel de Oliveira | 14 April 1991 | 20th | Amaro Cavalcante | 15 April 1991 |
| Rank | Player | Club | Goals |
|---|---|---|---|
| 1 | Rui Águas | Benfica | 25 |
| 2 | Domingos | Porto | 24 |
| 3 | Fernando Gomes | Sporting | 22 |
| 4 |  Ricky | Estrela da Amadora | 15 |
| 5 | Yekini | Vitória de Setúbal | 13 |
| Jorge Andrade | Boavista | ||
| 7 | Geraldão | Porto | 12 |
 Curcic | Farense | ||
| 9 | Rudi | Chaves | 11 |
| Marlon Brandão | Boavista | ||
| Tozé | Salgueiros |
