The 1991 Philippine Basketball Association (PBA) First Conference was the opening conference of the 1991 PBA season. It started on February 17 and ended on May 19, 1991. The tournament allows one-import each per team.

The following format will be observed for the duration of the conference:

• The teams were divided into 2 groups.

• Teams in a group will play against each other once and against teams in the other group twice; 11 games per team; Teams are then seeded by basis on win–loss records. Ties are broken among point differentials of the tied teams. Standings will be determined in one league table; teams do not qualify by basis of groupings.^[1]
• The top five teams after the eliminations will advance to the semifinals.
• Semifinals will be two round robin affairs with the remaining teams. Results from the elimination round will be carried over. A playoff incentive for a finals berth will be given to the team that will win at least five of their eight semifinal games.^[2]
• The top two teams (or the top team and the winner of the playoff incentive) will face each other in a best-of-seven championship series. The next two teams will qualify for a best-of-five playoff for third place.