Police are investigating the discovery made early this morning on the M9 in central Scotland.
An inquiry is under way into the circumstances of the death of the woman, who has not been identified.
Two blue police tents were set up on the route near the Bannockburn interchange.
The M9 was closed northbound between junction 9 Pirnhall and junction 10 Craigforth as well as the M80 at junction 9 northbound, causing motorists significant delays.
A Central Scotland Police spokeswoman said: "The body of a young woman was found earlier today on the M9 near to Bannockburn interchange and the circumstances surrounding her death are being investigated.
"To allow this to happen the northbound carriageway on the M9 will remain closed from junction 9 Bannockburn interchange."
Police said the body was discovered by a passing motorist at about 7am on the road under a bridge close to Bannockburn interchange, Stirling.
Chief Inspector Gordon Dawson said: "We are keen to hear from anybody who was on the M9 between 6.15am and 7am.
"We are particularly keen to hear from anybody who may have seen a young woman close to the motorway or on Birkhill Road bridge in Cambusbarron which crosses the motorway.
"The motorway is generally quiet at this time of the morning with commuter traffic but busier with heavy good vehicles, and we are keen to hear from any driver or operator who had vehicles in the area around this time.
"I also thank motorists for their patience to allow the investigation to continue."
Anyone with information can contact Central Scotland Police on 01786 456000.