A 25-year-old woman discovered she was switched at birth after a visit to donate blood revealed her "mother" was not biologically related to her.
The unnamed woman, from Graz in Austria, and her family are now accusing the hospital where she was born of incompetence.
On donating blood, the clinic told her she had a different blood type to both her parents and could not be related to them.
This revelation was later confirmed by a DNA test.
According to a report by Kleine Zeitung, the two babies were mixed up between October 15 and November 20 in 1990.
A total of 200 baby girls born in the University Hospital at Graz during this period have all been invited to take a voluntary DNA test to see if they were switched.
So far, the appeal has only yielded four volunteers.
The university hospital insisted there was currently no evidence its staff made any mistake.
Gebhard Falzberger, a director at the hospital, said: “We are making every effort, together with the affected family, to solve this case.
“If it can be proven that it was our fault, then I want to apologise to all concerned on behalf of the clinic.”