Four sites have been targeted in south Wales in the past year, including Royal Glamorgan Hospital in Talbot Green, near Llantrisant.
A car bonnet and a grill was stolen from a white Citreon DS3 there on Thursday between 8.30am and 4.00pm, Wales Online says.
In a separate incident, a bonnet was also stolen off a white Ford Fiesta.
Ellie Kinson works at the hospital and was a passenger with her colleague in the Citroen.
She finished work and arrived at the car to see the window smashed so the bonnet could not be opened.
“My colleague parked her car in the car park around 8:30 roughly, and we finished work at approximately 4pm,” the 25-year-old woman said.