Mattia Martinello, who is from Padua, northern Italy, was in Rome with some friends to celebrate his 18th birthday on Sunday, Il Messaggero reported.
After a night out the group of friends made their way to the Colosseum at around 5.00am to take some photos.
But as the teenager tried to climb over the fence with his friends to reach the monument he lost his balance and fell five metres, hitting his head.
Martinello was then taken to San Giovanni hospital where he is in a medically induced coma. He suffered internal bleeding and injuries to his head and chest.
It is not yet clear whether he has suffered any spinal damage.
The ‘selfie’ craze - of people taking photographs of themselves and posting them on social media websites - has gained global popularity but has had deadly consequences in recent months.
In June an Italian teenager died after she tried to take a selfie at the seaside, but slipped and fell 20 metres onto the rocks below.
In March, a 21-year-old Spanish man died after climbing on top of a train to take a selfie with friends. He was struck with a 3,5000-volt electric shock after touching a wire and died instantly.