The woman, from Utah, USA, became ill as she returned to the boat on which she and her friends had travelled to the dive site.
Police said they received a report shortly after 9am Thursday morning, 1 March, that the woman had completed her dive and, as she was getting back on board the boat, she began feeling unwell and lost consciousness.
Dive staff on the boat performed CPR as they transported her back to North West Point Dock, West Bay, where they were met by emergency services.
She was taken to the Cayman Islands Hospital where she was pronounced dead.
The victim had been vacationing on Grand Cayman with family members.
Enquiries into the death are ongoing, police said.