1989–90 Isthmian League

The 1989–90 season was the 75th season of the Isthmian League, which is an English football competition featuring semi-professional and amateur clubs from London, East and South East England.

The league consisted of three divisions. Division Two was divided into two sections.

Slough Town were champions, winning their second Isthmian League title and were promoted to the Conference.

Premier Division
The Premier Division consisted of 22 clubs, including 19 clubs from the previous season and three new clubs:
 * Aylesbury United, relegated from the Football Conference
 * Basingstoke Town, promoted as runners-up in Division One
 * Staines Town, promoted as champions of Division One

Division One
Division One consisted of 22 clubs, including 16 clubs from the previous season and six new clubs:

Two clubs relegated from the Premier Division:
 * Croydon
 * Tooting & Mitcham United

Two clubs promoted from Division Two North:
 * Harlow Town
 * Purfleet

Two clubs promoted from Division Two South:
 * Dorking
 * Whyteleafe

Division Two North
Division Two North consisted of 22 clubs, including 19 clubs from the previous season and three new clubs:


 * Basildon United, relegated from Division One
 * Collier Row, relegated from Division One
 * Finchley, transferred from Division Two South

Division Two South
Division Two South consisted of 21 clubs, including 18 clubs from the previous season and three new clubs:


 * Abingdon Town, joined from the Spartan League
 * Bracknell Town, relegated from Division One
 * Malden Vale, promoted from the Combined Counties League