The 1990–91 Primera División season was the second category of the Spanish basketball league system during the 1990–91 season.
A total of 16 teams contested the league, including 10 sides from the 1989–90 season, two relegated from the 1989–90 ACB and four promoted from the Segunda División.
CAB Obradoiro was not admitted by the FEB and was replaced by Loyola Easo, who obtained a relegation place the previous season.
Semifinal winners are promoted to Liga ACB.
Winners remain in the category next season and the losers play the second round of the relegation play-off.