The 51-year-old victim, who has cerebral palsy and walks with the use of a frame, answered a knock at his door in McKillop Place, Saltcoats, North Ayrshire, at about 7pm yesterday.
When he opened the door a man knocked him to the ground and threatened him, demanding cash.
The victim had no money on him but the thief stole some personal items from the house.
The 51-year-old was not injured and police are appealing for any witnesses who were in McKillop Street around the time of the incident last night.
The suspect is white, Scottish, aged between 20 and 30 and about 5ft 7ins. He was wearing a grey hooded top and grey tracksuit bottoms.
Detective Constable Fionntan Rankin said: "This was a despicable crime, carried out by a coward who targets vulnerable members of our society.
"I would appeal to anyone who was in the area of McKillop Place on Monday evening and saw anyone hanging about or answering the description of the suspect to come forward.
"Equally, anyone who has heard anything or thinks they know who is responsible to speak to the police."
Anyone with information can contact police on the non emergency number 101 or anonymously via Crimestoppers on 0800 555 111.