He could make his debut for Milan on Sunday at Serie A bottom side Ascoli.
What kind of reception awaits him in Italy is uncertain.
Ronaldo, who inspired Brazil to World Cup victory in 2002 and holds the
record for goals scored in World Cup tournaments with 15, played for his new
club's rivals Inter from 1997 to 2002.
The transfer makes him the 10th foreign player to play for both Inter and
Milan, joining a select group that includes Clarence Seedorf, Hernan Crespo,
Edgar Davids and Patrick Vieira.
None of them, however, aroused the same ill-feeling Ronaldo is likely to meet
when he pulls on the famous red and black shirt.
He needed a police escort to protect him from Inter fans when he left for
Madrid in 2002.
His return to Italy on Tuesday was low-key. He made no comment to reporters
as he slipped out of a side exit at Milan's Linate airport.
In a separate but related deal, media reports say Real Madrid are close to
signing Milan's Brazilian striker Ricardo Oliveira on loan until the end of the
The 26-year-old, who has scored just two league goals since joining Milan
from Real Betis for a fee of 17.5 million euros on the final day of the close
season window, was left out of the Milan squad for Wednesday's Italian Cup
semi-final against AS Roma.
Factbox on Ronaldo
* Born, September 22 1976 on outskirts of Rio de Janeiro.
* Together with Zinedine Zidane, he is the only player to have won the FIFA
World Player of the Year award on three occasions (1996, 1997 and 2002). He has
also won the European Footballer of the Year award twice (1997 and 2002).
* Won two World Cups (1994 and 2002) with Brazil and holds the record for
goals scored in World Cup tournaments with 15.
* Won his first cap for Brazil as a 17-year-old and has gone on to score 62
goals in 97 international appearances.
* Suffered a mysterious illness hours before the 1998 World Cup final in
France but after first being named as a substitute, he was included in the
starting line-up. He played badly and Brazil lost 3-0 to France.
* Has had problems with his knees throughout his career, undergoing surgery
while at PSV Eindhoven, Inter Milan and Real Madrid. Spent almost two years out
of the game while recovering from surgery after his knee buckled in the Italian
Cup final against Lazio in April 2000.
* His best season came at Barcelona in 1996-97 when he scored 45 goals in 48