A pickpocket described as a man in his thirties pinched an elderly man's wallet before running off.
The 89-year-old man was walking along Oliver Street between 12.45pm and 1pm when another man stopped him and asked for the time, to which he responded and continued walking.
A short time later the same man walked past him and took his wallet from his jacket pocket before running off along Oliver Street and onto Kingsley Park Terrace.
A Northamptonshire Police spokeswoman said: "The offender is described as a 6ft, 30-year-old white man, wearing a yellow or pink woolly hat."
Witnesses can contact police on 101 or Crimestoppers anonymously on 0800 111 555.