Online registration will close at midday on Friday, September 12, for the event – which takes place on Sunday, September 14.
However, you will still be able to register on the day if you would like to take part.
Around 500 participants are expected to join this year’s challenge, which has a five, nine or 18 mile walk to choose from.
Transport between routes is generously provided by Arriva buses with all drivers on the day volunteering their time for free.
All routes start and finish at Princes Risborough School in Merton Road, Princes Risborough.
Rennie Grove events manager Ruth Proudfoot said: “We’re very grateful to everyone who is supporting this year’s event, which will help us to continue caring for patients and families across the Chilterns.
“It’s a great day out for the whole family, including dogs, to walk the chalk and raise money to help local people at the same time.”
In 2013, the Chilterns 3 Peaks Challenge raised more than £30,000 – enough to fund a specialist hospice at home nurse for a year.
Participants are again encouraged to raise as much sponsorship as they can so that the total can be even higher this year.
A prize will go to the person who has raised the most sponsorship.
Registration for the Chilterns 3 Peaks Challenge is £20 for adults and £10 for children (anyone aged five to 16 years old), with under-5s going free.
The entry fee will cover the costs of putting on the event and includes a Chilterns 3 Peaks T-shirt, a medal on completion and water along the route.
Walkers taking part in the 18-mile route must register on the day between 9.30am and 10.30am. Nine and five mile walkers can register between 10am and 11am.
Volunteers are also needed to help give out medals at Ivinghoe Beacon when walkers cross the finishing line.