A woman has been airlifted to safety after slipping on steep ground, at Balscadden, on Dublin's Howth Head.
She has been transferred to Beaumont Hospital with head injuries.
Fergus Cooney from Howth Coast Guard said the Rescue Helicopter 116, the RNLI lifeboat, and paramedics from Dublin FireBrigade were called to the scene after the hillwalker got into difficulty this afternoon.
"It is one piece of advice we do say to people - stay to the main path in Howth," said Mr Cooney.
"Stick to that path the whole way around and you'll be okay.
"When you do deviate away from the main path, some of the conditions are quite treacherous.
He added: "If people see other members of the public that they think might be getting into trouble, just make that call straight away.
"Dial 112 or 999 and ask for the coastguard."