| 1990-91 ACB season | |
| League: | Liga ACB |
| Sport: | Basketball |
| Duration: | September 19, 1990 - May 30, 1990 |
| No Of Teams: | 24 |
| Tv: | Televisión Española |
| Season: | Regular Season |
| Season Champs: | Montigalà Joventut |
| Playoffs: | Playoffs |
| Playoffs Link: | 1991 ACB Playoffs |
| Finals: | ACB Finals |
| Finals Link: | 1991 ACB Playoffs#Finals |
| Finals Champ: | Montigalà Joventut |
| Finals Mvp: |  Corny Thompson |
| Finals Mvp Link: | ACB Finals Most Valuable Player Award |
| Seasonslistnames: | ACB |
| Prevseason Link: | 1989–90 ACB season |
| Prevseason Year: | 1989–90 |
| Nextseason Link: | 1991–92 ACB season |
| Nextseason Year: | 1991–92 |
The 1990–91 ACB season was the 8th season of the Liga ACB, after changing its name. The competition format changed again. The 24 teams were divided in two groups of 12 teams each. The eight first teams of each group advanced to the championship playoffs, and the four last teams of each group advanced to the relegation playoffs.
Montigalà Joventut won their first ACB title, and their 3rd overall. It was the first ACB title won by a team besides FC Barcelona and Real Madrid.
| width=10px bgcolor=#ccffcc | Advanced to Championship Playoffs | ||
| width=10px bgcolor=#ff6666 | Advanced to Relegation Playoffs |
| width=175 | Team | width=20 | width=20 | width=20 | width=20 | width=20 | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| Montigalà Joventut | 34 | 30 | 4 | 3091 | 2550 | ||||||
| Estudiantes Caja Postal | 34 | 25 | 9 | 2862 | 2637 | ||||||
| CAI Zaragoza | 34 | 20 | 14 | 3135 | 2929 | ||||||
| Fórum Valladolid | 34 | 20 | 14 | 2722 | 2695 | ||||||
| Valvi Girona | 34 | 18 | 16 | 2695 | 2668 | ||||||
| Mayoral Maristas | 34 | 16 | 18 | 2665 | 2664 | ||||||
| Caja San Fernando | 34 | 15 | 19 | 2759 | 2812 | ||||||
| Caixa Ourense | 34 | 15 | 19 | 2749 | 2984 | ||||||
| Grupo IFA | 34 | 14 | 20 | 2712 | 2819 | ||||||
| Elosúa León | 34 | 13 | 21 | 2854 | 2846 | ||||||
| Cajacanarias | 34 | 10 | 24 | 2820 | 3055 | ||||||
| Puleva Baloncesto Granada | 34 | 9 | 25 | 2534 | 2899 |
| width=175 | Team | width=20 | width=20 | width=20 | width=20 | width=20 | |||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| FC Barcelona | 34 | 26 | 8 | 2822 | 2443 | ||||||
| Real Madrid Otaysa | 34 | 24 | 10 | 2745 | 2575 | ||||||
| Taugrés | 34 | 21 | 13 | 2796 | 2669 | ||||||
| Atlético Madrid Villalba | 34 | 17 | 17 | 2648 | 2744 | ||||||
| Huesca La Magia | 34 | 16 | 18 | 2647 | 2612 | ||||||
| Pamesa Valencia | 34 | 15 | 19 | 2615 | 2628 | ||||||
| Caja Ronda | 34 | 15 | 19 | 2435 | 2534 | ||||||
| Dyc Breogán | 34 | 15 | 19 | 2549 | 2667 | ||||||
| Zumos Júver Murcia | 34 | 15 | 19 | 2704 | 2755 | ||||||
| TDK Manresa | 34 | 15 | 19 | 2625 | 2752 | ||||||
| Cajabilbao | 34 | 12 | 22 | 2782 | 2911 | ||||||
| OAR Ferrol | 34 | 12 | 22 | 2571 | 2689 |
Cajabilbao and Cajacanarias were relegated.
See main article: 1991 ACB Playoffs.