The 1990–91 season was Sport Lisboa e Benfica's 87th season in existence and the club's 57th consecutive season in the top flight of Portuguese football, covering the period from 1 July 1990 to 30 June 1991. Benfica competed domestically in the Primeira Divisão and the Taça de Portugal, and participated in the UEFA Cup after finishing second in the previous league.

With only a Supertaça Cândido de Oliveira won in the past season, Benfica was keen on retake the Primeira Divisão title again. They were quickly eliminated from Europe at the hands of Roma, so all attentions were pointed on the league title. A strong campaign witnessed Benfica overtake Porto in February and then close the title with an away win in the Clássico, a controversial match because of the tactics employed by Porto to destabilize the team. On late May, Benfica secured their 29th league title, while Rui Àguas won the Bola de Prata for league top-scorer.

Benfica started the new season after having lost their fifth European Cup Final in the past season, while Porto regained the league title back. Swedish manager Sven-Göran Eriksson made some squad adjustments, releasing established players like Fernando Chalana, Diamantino Miranda and Álvaro Magalhães, and losing Aldair to Roma. He nearly lost Valdo too, but Benfica and Fiorentina failed to agree terms. To counter the departures, he brought back Rui Águas, from Porto,Neno from Vitória de Guimarães, alongside William, and also added Isaías and Stefan Schwarz.Tomas Brolin was also a target but Eriksson thought he was not ready to play for a club like Benfica.

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