Top Gear host Jeremy Clarkson breached BBC guidelines by comparing a Japanese car to people with growths on their faces.
A report by the BBC Trust's editorial standards committee (ESC) found he "strayed into an offensive stereotypical assumption" with the scripted remarks during an episode of the hit motoring show.
A member of the public complained about the "offensive" remarks after Clarkson likened the shape of a Prius campervan to someone with "a growth on their face" and referred to it as the "elephant car".
He also described it as "not a car that you could talk to at a party unless you were looking at something else".
The ESC said the show's audience enjoyed the presenters' "sometimes controversial and forthright views" but ruled this remark "played on a stereotypically negative reaction to facial disfigurement".