Adelaide City were the defending champions, having defeated Sydney Olympic to win their second title in the previous year's final, but they were eliminated in the semi-finals by eventual winners South Melbourne.
[1] South Melbourne defeated Sydney Olympic 4–1 in the final to win their first NSL Cup title.
[2] The NSL Cup was a knockout competition with 14 teams taking part all trying to reach the Final in April 1990.
[3] The competition consisted of the 14 teams from the National Soccer League.
APIA Leichhardt and Blacktown City had a bye for the First round.