An elderly man was airlifted to Treliske after collapsing on the deck of the Scillonian yesterday.
Paramedics were dropped on to the ship to assess the man, who had hit his head on railings.
They decided to wait until the Scillonian had docked at St Mary's before trying to take the patient to the Royal Cornwall Hospital at Treliske, Cornwall Live reports.
The coastguard helicopter was called at 10.51am to airlift him back to the mainland.
A spokesman for the coastguard said: "We assisted in escorting a casualty who had injured their head on board the Scillonian."
Isles of Scilly Travel said: "It was excellent teamwork by everyone on board the ship."