Officers at the Inverness music event say they suspect the man, from Edinburgh, may have taken drugs.
A 19 year-old woman and a 20 year-old man were also hospitalised after taking “substances”.
Emergency services were called to the young man from Edinburghcollapsed in the main arena at RockNess, late last night.
He was taken to the hospital tent and stabilized before being transferred to Raigmore Hospital. But he failed to respond to treatment and died during the early hours of this morning.
Early indications are that the man may have consumed drugs and this is one of the lines of enquiry at this stage. A post mortem will be carried out to determine the cause of death.
The other festival goers remain in hospital and their condition is not life-threatening.Police and organisers have minimised the risk of controlled drugs at the festival through a range of measures, including searches and the use of drugs dogs, as well as amnesty bins.
Police are currently making enquiries into a “legal high” substance known as BENZO FURY which is believed may have been taken by those who are currently being treated in hospital.
Event Commander, Superintendent Stevie Mackay said: “Taking drugs or any medicines, which you have not been prescribed, is an extremely risky thing to do. People may think that legal highs are safe, because they are not classed as a controlled drug, but they are extremely dangerous.
“If anyone has the tablets described or any other drug, whether controlled or a “legal high”, in their possession, they are advised not to take them and to hand these in. Amnesty bins are available at the main Nesstival entrance or anyone can hand in substances to Crew 2000 at the WELFARE Tent.”
Public Health Constultant Dr Cameron Stark said: ” Our advice is simple: limit how much alcohol you drink, and don’t take non prescribed drugs. If however you have taken non prescribed drugs including “legal highs”, it is really important that you don’t combine them with alcohol. If you feel unwell or you are worried about a friend, please get immediate advice from the onsite medical team.”
Festival Organiser Jim King said “What should be very clear from this information is that legal highs does not mean safe, and customers should not go anywhere near these dangerous substances. Festival goers should heed the advice given to them by the health professionals and the police, and stay safe by avoiding drugs of any kind.”