The man was parked in Queensberry Street yesterday morning waiting for his wife to return when a young woman opened the passenger door, entered the car and engaged him in conversation.
The woman asked the man for directions to another part of Scotland.
Shortly after he gave advice she left the vehicle and he discovered the cash had been stolen.
Police say the car is a Ford Mondeo, and the incident took pace at about 10 am on Thursday.
The woman is described as being in her early to mid 20s, with dark hair, attractive and was wearing a floral dress.
She spoke with a foreign accent which may have been Spanish.
PC Ross Milligan at Dumfries said: “This is a very unusual modus operandi (MO) and one not heard of in this part of the country before.
“We are keen to speak to anyone who may have been around the Queensberry Street area, or in the town centre in general around 10 am to get in touch if they saw this female.
“Callers can speak to us on the 101 number.”