A 76-year-old man was tied up, threatened at knifepoint and punched in the face by robbers at his house in Mackworth, Derby.
Police believe two men broke into the back of the house on Brackensdale Avenue late on Tuesday night.
The intruders, described as white and wearing balaclavas, stole cash and financial documents.
Police were called at 0935 GMT by a visiting relative. The victim was taken to hospital with facial injuries.
Det Insp Mark Argyle said: "This was an extremely nasty ordeal for the victim and we are determined to track down the culprits."