Middlesex 4 was an English level 13 Rugby Union league with teams from north-west London taking part. Promoted teams moved up to Middlesex 3 and since the cancellation of Middlesex 5 at the end of the 1991–92 season there was no relegation. 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.