Arrest after girl, 17, dies from suspected drugs overdose at music festival
The suspect, also aged 17, was detained on suspicion of supplying controlled drugs.
Both teenagers are from the Oldham area, West Yorkshire Police said.
Officers were called to the Bramham Park site following a report that the girl had died shortly after 3.40am on Saturday.
Leeds Festival's police commander, Superintendent Matt Davison, said: "Our thoughts are with the family of the girl who has died. We have family liaison officers in place supporting them and they have asked that their privacy is respected at this extremely difficult time.
"While the exact cause of her death is yet to be established, the information we have indicates that she has taken a combination of drugs.
"This is a tragic incident and I hope serves as a timely reminder to others of the risk of taking illegal substances, particularly when mixing different types of drugs and drinking alcohol.
"If anyone has any concerns for either themselves or others at the festival, I would urge them to contact staff on-site or seek urgent medical assistance."
A day earlier the festival had posted a warning about "dangerous, high strength pills" in circulation at the site.
They wrote: "Donkey Kong, Trump and Skype pills have been found in circulation onsite. These are very dangerous, high strength pills, up to 3 times the normal average adult dose."
On its website, organisers state that the festival "does not condone the use of drugs", adding: "It is illegal to buy, sell or take drugs. Drugs enforcement laws are as applicable onsite as anywhere else in the UK."
Foo Fighters headlined the main stage at the annual festival on Friday night.
The 1975 are due to headline on Saturday, and Post Malone is top of the bill on Sunday.