The musical legend turned 80 in March (10) and to mark the milestone age, executives at the Henry Miller theatre in New York changed the venue's name to honour him.
Sondheim was visibly moved by the tribute as he was joined by his longtime collaborators Patti LuPone, Nathan Lane and John Weidman for the unveiling.
He says, "I'm deeply embarrassed. I'm thrilled, but deeply embarrassed. I've always hated my last name. It just doesn't sing."
And Lane paid tribute to his pal, adding, "He is a true gentleman of the theater, a theatrical legend."