A man robbed a woman motorist of $4900 while her car was idling at traffic lights, in Northmead on Wednesday.
The woman, 36 of Kellyville, and her son who was in the car with her, stopped at the intersection of the Cumberland Highway and Old Windsor Road about 7.45pm.
She said the man opened the passenger door, leaned into the car across her son and snatched her bag and wallet, worth $4900 in total.
She described the man as being dark-skinned, of Pacific Islander appearance, with facial hair, of large build, aged 30-35, and wearing a red cap.
Anyone with any information is urged to contact The Hills police on 9680 5399 or Crime Stoppers on 1800 333 000.