The singer is a patron of the Noah's Ark Appeal, a charity set up to fund the building, and it named the walkway outside the Cardiff hospital Dame Shirley Bassey Way.
However, the Welsh version on the sign says Ffordd Y Fonsig Shirley Bassey. The Welsh word for dame is Fonesig.
A Noah's Ark spokeswoman said action will be taken to rectify the mistake.
"It is a shame that this has detracted attention from the occasion," she added.
A new road sign in honour of Dame Shirley Bassey outside the Children's Hospital for Wales has a typo in it.