The 1990 NBL season was the ninth season of the National Basketball League. The league expanded to 12 teams in 1990, with Hutt Valley, Otago and Waitakere joining the ranks. Waitakere replaced the outgoing Waitemata after Waitemata City amalgamated to form Waitakere City. In addition, North Shore was renamed North Harbour. Canterbury won the championship in 1990 to claim their third league title. In the NBL's first all-South Island final, Canterbury prevailed over Nelson in a gripping game, winning 76–73 to go back-to-back.