An Audi Q7 was stolen, after it was left unattended with the engine running.
The car was taken from Spring Lane, Great Horwood at about 8.10am on Monday.
In recent days there have been a number of thefts from vehicles which have been left unlocked and unattended by motorists in Aylesbury Vale.
A Vauxhall Zafira was stolen from a communal parking area in Aylesbury yesterday, Thursday, after the driver left the car for a matter of seconds to get an ice-scraper from his home.
A memory stick was taken from an unlocked BMW 3 series in in Wendover on Tuesday or Wednesday.
Det Insp Joe Banfield, from Aylesbury CID, said: “Leaving car doors unlocked offers thieves the perfect opportunity.
“It only needs a moment for a thief to take items left in the car or jump behind the wheel and drive off.
“The simple message is not to leave a car with its engine running unattended for any length of time, whether it is left on your own driveway to de-ice on a cold winter morning or, for example, while you pop to post a letter or to pay for fuel.
“Give yourself extra time to defrost all of your cars windows and don’t be tempted to leave the car even for a few moments.
“As well as causing a huge amount of upset and stress, this type of theft can also result in your insurance company refusing to settle the claim because the vehicle was left unsecure.
“You could potentially lose thousands of pounds.”
Anyone with information can contact the Thames Valley Police Enquiry Centre on 101 or contact Crimestoppers anonymously on 0800 555 111.