1999 Tercera División play-offs
The 1999 Tercera División play-offs to Segunda División B from Tercera División were the final playoffs for the promotion from 1998–99 Tercera División to 1999–2000 Segunda División B. The first four teams in each group took part in the play-off.
Format
The 68 participating teams were divided into 5 series each made up of 4 groups in the category, with the exception of Series E , which was only formed by Group XII . Each series was divided into 4 groups formed by a 1st, a 2nd, a 3rd and a 4th classified from each group, which played a double-round playoff. Each victory was equivalent to 3 points, the tie to 1 point and the defeat to 0 points. The champion of each group obtained the promotion to Second Division B.The distribution of each series was as follows:
Teams for 1998–99 Play-Offs
Group I – Galicia  | Group II – Asturias  | Group III – Cantabria  | Group IV – Basque Country  | Group V – Catalonia  |
| 1st Porriño Industrial FC | 1st Club Marino de Luanco | 1st Racing de Santander B | 1st Real Sociedad B | 1st AEC Manlleu |
| 2nd RC Celta de Vigo B | 2nd Club Siero | 2nd UM Escobedo | 2nd Deportivo Alavés B | 2nd CE Premià |
| 3rd CCD Cerceda | 3rd Navia CF | 3rd Ribamontán al Mar CF | 3rd Real Unión de Irún | 3rd CE Europa |
| 4th Viveiro CF | 4th Real Titánico | 4th CD Bezana | 4th Zalla UC | 4th CE Mataró |
Group XI – Balearic Islands  | Group XII – Canary Islands  | Group XIII – Region of Murcia  | Group XIV – Extremadura  | Group XV – Navarre and La Rioja   |
| 1st CD Constancia | 1st UD Las Palmas B | 1st Orihuela CF | 1st CD Grabasa Burguillos | 1st Peña Sport FC |
| 2nd UD Poblense | 2nd UD Orotava | 2nd Lorca CF | 2nd SP Villafranca | 2nd CD Azcoyen |
| 3rd CD Ferriolense | 3rd UD Lanzarote | 3rd AD Mar Menor | 3rd CD Don Benito | 3rd CD Izarra |
| 4th CD Atlético Baleares | 4th UD Telde | 4th UD Horadada | 4th Mérida Promesas UD | 4th CD Logroñés B |