NHS Networks has announced that it is to cease operating on 31 October after running out of funding.
The organisation, which was founded in April 2005, was tasked with identifying existing networks and encouraging sharing of ideas.
More than 500 networks are listed in the NHS Networks register. Approximately a third of these do not have an online presence anywhere else, with around 20 operating private discussion forums via the site.
Although initially funded for two years only, it has managed to stretch its funding to keep running until the autumn by reducing its staff headcount from five to three and maintaining a low profile at conferences.
A spokeswoman said: "In the remaining months we will endeavour to find a new home for the website so that the valuable information which has been built up over the past three years is not lost. We will do everything we can to find new online homes for all networks that want one."