The 61-year-old man collapsed and injured himself near the top of Beinn Bhrotain in the Cairngorm Mountains at about 1pm.
A mountain rescue operation was launched and the man was airlifted by RAF helicopter to Raigmore Hospital in Inverness. He was pronounced dead on arrival.
The man, from Fife, was with a party of walkers from the central belt of Scotland who were able to call the emergency services for help.
The rest of the group, believed to include six teenagers and two adults, were taken off the mountain in a Land Rover by Braemar Mountain Rescue Team and returned to Braemar.
No one else in the group was injured.