The police said on Monday that the woman has been living in an extremely simple shelter for the past year, but appears to be in good physical shape.
The woman, whose name was not disclosed, is 52 and was reported missing in 1997 in the German state of Brandenburg, near Berlin.
Police said they did not know where she lived before moving to the woods in the community of Bolligen.
They said the owner of the land would soon tell the woman she must leave.
But if necessary the authorities will work with social services to reach an acceptable solution for the woman.