The seriously ill 86-year-old victim, who does not want to be named, parked her red Shoprider Perrero in the grounds of her sheltered accommodation in The Avenue, Eastbourne.
Roger Crawford, the elderly woman's nephew, says it was stolen at around 11.35pm on Saturday (November 22) and the theft was captured on the premises' CCTV.
He explained his aunt has to make regular hospital visits and had saved more than £1,000 to buy the scooter six months ago.
Mr Crawford said, "This has really upset me because it absolutely beggars belief.
"The CCTV footage shows him getting on the scooter and driving away, bold as brass.
"This man is a scumbag, what he has done is unforgivable and I hope he gets his comeuppance."
Mr Crawford explained his aunt was unable to insure the scooter because she has no garage facility at her accommodation.
"She is now immobile and won't get any money back," said Mr Crawford.
"As her closest family member, I will see if we can sort something out for her but we are talking about £1,000 and we are all suffering from the credit crunch at the moment."
The upset nephew hopes anyone with information will contact police.
A Sussex Police spokesperson said, "The elderly victim is understandably extremely upset by the theft of her scooter which she relied on for getting out and about.
"If anyone witnessed what happened or has any information then we would urge them to contact police as soon as possible."
Witnesses should phone 0845 60 70 999, quoting serial 639 of November 23.
juliet.perry@trbeckett.co.uk