1990–91 ACB season

The competition format changed again.

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.

Cajabilbao and Cajacanarias were relegated.