Penfriend charity Write Away, whose patrons include David Blunkett and newsreader Huw Edwards, is to close because of financial problems.
Last week, trustees took the decision to wind up the organisation "in the absence of any clear prospect of future sustainability and a real threat of insolvency".
Andy Grout, the organisation's chief executive, blamed a tough fundraising environment caused partly by the Asian tsunami and the Pakistani earthquake.
"We have tried very hard to find ways to keep the spirit and work of Write Away alive," he wrote to supporters. "But nothing has been forthcoming."
Since its launch in 1991, the charity has found penpals for more than 20,000 children and adults with special needs.