A 12-year-old boy is among 15 people who were arrested on the first day of the Reading Festival.
Police say a total of 87 offences were reported and the vast majority of crimes committed were possession of Class A drugs or thefts from tents.
Officers are urging anyone going to the festival to leave valuables at home or use the lockers at the Rivermead site.
About 80,000 music fans are due to attend each day of this year's event on Friday, Saturday and Sunday.
Supt Steve Hockin, of Thames Valley Police, said: "I would like to remind people not to buy tickets from touts as there is a serious risk that the tickets will be false and you will be wasting your money.
"It is a big risk," he said.