We look at 11 players who played for the Whites and Boro.
The goalkeeper came through the ranks at Middlesbrough, before moving to Chelsea in 2009. Spells at Doncaster Rovers and Barnsley followed, before a two year spell at Leeds, which came to an end last summer.
Arguably the best defender to come through the ranks at Thorp Arch, after starring for Leeds he had spells at Newcastle United and Real Madrid. He went on to have two spells at Middlesbrough.
Signed by Middlesbrough in 2000, Ehiogu made over 150 appearances for the club over a seven year period. He had a short spell at Leeds on loan from the Riverside in the 2006/07 season.
The full-back was signed by Leeds from Charlton Atheltic in 1999 and went on to win 19 caps for England. He spent the 2003/04 season on loan at Middlesbrough, helping them win the League Cup.
A product of Manchester City, Clayton was signed by Simon Grayson at Leeds in 2010. He re-joined Grayson at Huddersfield Town two years later, before joining Middlesbrough, helping them reach the Premier League in 2016.
The midfielder helped Middlesbrough win promotion to Premier League from the Championship during the 2015/2016 season. In total Forshaw made over 100 appearances during his time at the Riverside before joining Leeds in January.
After coming through the ranks at Leeds, Whelan moved to Coventry City, linking up with former team-mate Gordon Strachan, before joining Middlesbrough. You can hear him regularly now as a pundit on BBC Radio Leeds.
Signed by Geroge Graham from Boavista, Hasselbaink was an instant success at Leeds. He moved to Atletico Madrid in 1999, before returning to England with Chelsea. He later had spells at Middlesbrough, Charlton Athletic and Cardiff City.
The Australian was brought to Leeds in 2000 from Celtic and enjoyed a successful time at Elland Road. After the Leeds were relegated in 2004, he joined Middlesbrough, before finishing his career at Newcastle United.