Ten Tors has been cancelled as coronavirus restrictions will still be in place when it was due to take place.
The challenge was due to take place on Dartmoor in May 2021, but organisers have announced its cancellation.
The British Army, which organises the challenge for thousands of young people from across the South West, says arrangements are being made for a virtual event to keep the 'Ten Tors flame alive' and plans are already underway for 2022.
In a statement Ten Tors secretary, Colonel Neville Holmes, said: "It is with regret that I have to announce it is no longer possible to hold a physical Ten Tors event on Dartmoor this May.
"As you know, we have been working closely with the local authorities and Ten Tors Policy Committee to plan a safe and enjoyable event but the restrictions that will still be in place over that period mean this is no longer possible.
"I know this will be a huge disappointment to many, however, given that safety is always our number one priority, I hope you understand.
"We are planning to enable a virtual event which teams may wish to conduct closer to home during 2021 to keep the Ten Tors ‘flame alive’ and if so, please look out for more details to follow shortly.
"I can also confirm plans are already well underway to run a full Ten Tors event in May 2022 and look forward to seeing you all then.
"In the meantime, I would like to take this opportunity to thank you all for your forbearance and to hope you and your families stay safe and well."
2,400 people from schools, colleges, Scout groups at Cadet squadrons from across the South West of England take part in the Ten Tors weekend hike in early May each year.
It has been running since 1960 and involves teams of six young people from across the South West of England who hike to checkpoints on ten specified tors on Dartmoor.