No teams were added, removed, or relocated in the 1991 season.
However, the MILL did divide the six teams into two divisions: Detroit, Pittsburgh, and New England comprised the National Division, and the American Division was Baltimore, New York, and Philadelphia.
Reference: [2] x: Clinched playoff berth; c: Clinched playoff berth by crossing over to another division; y: Clinched division; z: Clinched best regular season record; GP: Games PlayedW: Wins; L: Losses; GB: Games back; PCT: Win percentage; Home: Record at Home; Road: Record on the Road; GF: Goals scored; GA: Goals allowedDifferential: Difference between goals scored and allowed; GF/GP: Average number of goals scored per game; GA/GP: Average number of goals allowed per game The first-ever MILL All-Star Game was held at the Spectrum in Philadelphia during the 1991 season.
Italics indicate tied single-season records.
10,814 were in attendance at Baltimore Arena to see the visiting Detroit Turbos defeat the Baltimore Thunder in the championship game.