Cassano, 18, is regarded as one of Italy's brightest prospects and has signed a five-year deal that will earn him around £12 million. Roma also secured the rights to market his image and said in a statement they will turn him into "A symbol of the AS Roma brand".
At the beginning of February, Roma president Franco Sensi said the club had signed the youngster despite strong interest from Juventus and English champions Manchester United.
Cassano, who was born on the day Italy won the 1982 World Cup, likes to play behind the strikers, but faces the task of dislodging Roma crowd favourite Francesco Totti from the side.
It could also see the end of Hidetoshi Nakata's spell at the club as he is regarded as second-choice to Totti, and he may move on should Roma coach Fabio Capello be unable to guarantee the Japanese ace regular first-team action.
The move is a dream come true for Cassano, who said it would be a dream to play alongside his idol Totti.
