The 1991 Tercera División play-offs to Segunda División B from Tercera División (Promotion play-offs) were the final playoffs for the promotion from 1990–91 Tercera División to 1991–92 Segunda División B. The champion of every group (excluding reserve teams) took part in the play-off.
The teams play a league of four teams, divided into 17 groups of 5 zones.
Zone A: 4 groups with teams of Comunidad de Madrid (3ª Gr. 7), Galicia (3ª Gr. 1), Asturias (3ª Gr. 2) & Castilla y León (3ª Gr. 8).Zone B: 4 groups with teams of Aragón (3ª Gr. 16), País Vasco (3ª Gr. 4), Navarra+La Rioja (3ª Gr. 15) & Cantabria (3ª Gr. 3).Zone C: 4 groups with teams of Región de Murcia (3ª Gr. 13), Baleares (3ª Gr. 11), Comunidad Valenciana (3ª Gr. 6) & Cataluña (3ª Gr. 5).Zone D: 4 groups with teams of Extremadura (3ª Gr. 14), Castilla-La Mancha (3ª Gr. 17) & Andalucía (3ª Gr. 9 & 10)Zone E: 1 group with teams of Islas Canarias (3ª Gr. 12).The champion of each group is promoted to Segunda División B.
