Around 80,000 fans were at the home ground, the Bernabeu, to welcome Ronaldo following his record transfer.
The current world player of the year was signed by the Spanish giants from Manchester United in a deal worth £80m.
The Portuguese international had passed a medical examination earlier in the day to complete his move.
He told supporters: "I am just so happy to be here. For me, I have made my childhood dream a reality, which was nothing less than playing for Real Madrid.
"I didn't expect a jam-packed stadium - this is truly impressive."
Ronaldo then led the crowd into a cry of "Viva Madrid!"
The forward, who signed a six-year contract, has been given the number nine shirt - the same as Madrid great Alfredo di Stefano.
The 24-year-old was greeted by Di Stefano as well as Portuguese legend Eusebio and Florentino Perez, the club president whose re-election prompted his signing from United.
Ronaldo is the jewel in the crown of Perez's self-styled "spectacular sporting project".
After bringing "galacticos" David Beckham, Zinedine Zidane and Luis Figo to the club during his previous term, Perez has spent around £185m on Ronaldo, Brazilian playmaker Kaka, French striker Karim Benzema and defender Raul Albiol.
He is hoping the signing of such high-profile players will help Real take the Spanish and European Champions League crowns from arch-rivals Barcelona.
He also aims to boost revenue via the sale of replica merchandise and marketing rights.
Madrid had been chasing Ronaldo since 2006. He won the third of three successive Premier League titles last season.
Fans had queued outside the Bernabeu from early on in the day to catch a glimpse of their latest star.