Middlesex 1 was an English level 10 Rugby Union league with teams from north-west London taking part.

The division was cancelled in at the end of the 1995–96 campaign after nine seasons due to the merger of the Hertfordshire and Middlesex regional leagues.

When league rugby began in 1987 this division contained the following teams: The original Middlesex 1 was a tier 8 league with promotion up to London 3 North West and relegation down to Middlesex 2.

The creation of Herts/Middlesex at the beginning of the 1992–93 season meant that Middlesex 1 dropped to become a tier 9 league.

The introduction of National 5 South for the 1993–94 season meant that Middlesex 1 dropped another level to become a tier 10 league for the years that National 5 South was active.