The Rei Momo, or Carnival King, officially kicked off five days and nights of nonstop partying Friday with a special appeal for revelers to practice safe sex.
"I wish all my subjects peace and health, that they celebrate safely and remember that the condom is the best Carnival costume," said Carnival King Alex Oliveira as he received the key to the city from Vice Mayor Otavio Leite.
Brazil's Carnival is traditionally a time of wild partying and reckless abandon, but in recent years the government has made AIDS prevention a major feature of the annual celebrations, using puns and word games to promote safe sex.
The Health Ministry plans to distribute some 25 million condoms this year, more than double the 11 million condoms distributed last year, at celebrations across this nation of 185 million people.
Even before the official start, samba bands have jammed traffic on city streets for weeks.
The centerpiece of Brazil's Carnival is the annual samba parade, which takes place Sunday and Monday nights in the city's Sambadrome stadium.
The parade features the city's 14 top samba groups and is beamed across the nation on live television.
Each group spends up to $2 million to stage an 80-minute-long parade featuring up to 5,000 dancers, hundreds of drums and a dozen magnificent floats in an effort to win the title of Carnival champion.
And while the distinction brings little more than bragging rights, fans root for their favorite groups with a passion usually reserved for top soccer teams.
But there's more to Carnival than the parade. More than ever, the party is taking place in the streets.
Officials said they expected some 600,000 tourists for this year's Carnival celebrations in Rio de Janeiro.