1999–2000 National League 1

The 1999–2000 National League 1, sponsored by Jewson, was the thirteenth full season of rugby union within the third tier of the English league system.

Structure
The league consisted of fourteen teams, playing each other on a home and away basis to make a total of twenty-six matches for each team. There were two promotion places with the top two teams promoted to the newly named 2000–01 National Division One (previously known as the Allied Dunbar Premiership Two). Two teams were relegated to either National League 2 North or South, depending on geographical location.

Participating clubs
Ten of the clubs participating in last seasons competition. To make up the numbers two of the teams (Birmingham & Solihull and Manchester) were promoted from National 2 North, and two from National 2 South (Camberley and Henley) were also promoted.

Sponsorship
National League 1 is sponsored by the building suppliers, Jewson.