The man was at home around 4.30pm this afternoon when a dark coloured jeep drove up to his front door in the Ballinamore area of Fintown.
A man in his 20s knocked and asked for a jug of water.
When the pensioner went into the kitchen of his home to answer what he thought was a good errand for someone in need, the thief struck.
He walked into the house and lifted money which had been sitting on a table.
When the pensioner returned, the burglar had fled.
A text alert on the incident was sent out in the area over an hour later.
Gardai in Glenties have spent this evening trying to locate the thief.
“This was a particularly despicable crime,” said one shocked neighbour.
“The victim is one of the gentlest and nicest people you could ever hope to meet and someone has taken advantage of that generosity.”