The 19-year-old man was hit by a black cab on George IV Bridge at around 2.20am on Saturday.
He was taken to the Western General Hospital by ambulance.
A spokeswoman for Lothian and Borders Police said: "The injured party sustained serious injuries and is being treated within the Western General Hospital."
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Hide AdGeorge IV Bridge was closed following the incident, and reopened at around 7.15am on Saturday.
Lothian and Borders Police appealed for any witnesses.