The 1998–99 Primeira Divisão was the 65th edition of top flight of Portuguese football. It started on 23 August 1998 with a match between Chaves and Académica Coimbra, and ended on 30 May 1999. The league was contested by 18 clubs with Porto as the defending champions.
Porto won the league and qualified for the 1999–2000 UEFA Champions League group stage, along with Boavista, who qualified for the third round. With the extinction of the UEFA Cup Winners’ Cup, the Taça de Portugal winner qualified for the UEFA Cup, so Beira-Mar joined Benfica, Sporting CP and Vitória de Setúbal in the 1999-2000 UEFA Cup; in opposite, Beira-Mar, Chaves and Académica Coimbra were relegated to the Liga de Honra. Mário Jardel was the top scorer with 36 goals.
Leça, Varzim and Belenenses, were consigned to the Liga de Honra following their final classification in 1997–98 season.
The other three teams were replaced by União de Leiria, Beira-Mar, Alverca from the Liga de Honra.