The 1991 Philippine Basketball Association (PBA) All-Filipino Conference was the second conference of the 1991 PBA season. It started on June 9 and ended on September 1, 1991. The tournament is an All-Filipino format, which doesn't require an import or a pure-foreign player for each 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.^[2]
• Semifinals will be two round robin affairs with the remaining five teams. Results from the eliminations 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.
• The top two teams (or the top team and the winner of the playoff incentive) will face each other in a best-of-five championship series. The next two teams (or the loser of the playoff incentive and the fourth seeded team) dispute the third-place trophy in a best of three playoff.