The Dutch Eerste Divisie in the 1990–91 season was contested by 20 teams, one more than in the previous season. This was due to VC Vlissingen entering from the amateurs. De Graafschap won the championship.

Entering from amateur football

Relegated from the 1989–90 Eredivisie

DS '79 changed their name to Dordrecht '90 this season.

The promotion/relegation play-offs consisted of three rounds. In the group round, four period winners (the best teams during each of the four quarters of the regular competition) and two (other) best placed teams in the league, played in two groups of three teams. The group winners would play in play-off 1. The winners of that play-off would be promoted to the Eredivisie, the loser had to take on the number 16 of the Eredivisie in play-off 2. These two teams played for the third and last position in the Eredivisie of next season.

Play-off 1

VVV-Venlo: promoted to Eredivisie
NAC Breda: play-off 2

Play-off 2