CLIC Sargent has launched a new campaign called Wise Up Your Wardrobe, which asks people to clear out any clothes they will never wear, including unwanted Christmas gifts.
The clothes can be sold on eBay and the profits donated to CLIC Sargent, which provides clinical, practical and emotional support to children and young people with cancer.
Anything from 10% to 100% of the sales value can be donated, but all items must be new with their tags still attached. People can also drop clothes into any CLIC Sargent shop and the items will be sold on eBay on their behalf.
Twiggy has donated an unworn leather jacket to be sold on the online auction site.
She said: "I am delighted to support CLIC Sargent's new and innovative eBay campaign, Wise Up Your Wardrobe.
"It's a fantastic and easy way to turn your unworn clothes into cash while also raising money to help support children and young people with cancer, and their families. I am keen to encourage as many people as possible to get involved."
CLIC Sargent eBay co-ordinator Kate Apperley said: "It is great to have Twiggy supporting our campaign and I hope it inspires other people to sell their unworn items that are sitting at the back of their wardrobe too.
"There couldn't be a better reason to have a January clear out. And it will help us to provide clinical, practical and emotional support to children and young people living with cancer."
For more information about buying or selling unworn clothes, visit www.clicsargent.org.uk/wiseupyourwardrobe.