The 26-year-old woman, who has not been named, had stopped and parked her blue Toyota Aygo in a lay-by when she was struck by a passing black Range Rover.
The accident happened on the northbound carriageway of the Perth to Inverness road near to Auchterarder at 11.30pm last night.
A Police Scotland spokesman said: “As a result of the collision the female was taken to Ninewells Hospital in Dundee, where she is being treated for a serious injury to her left leg. Anyone who may have witnessed the incident or who has any information should phone Police Scotland on 101 or speak to any officer.”