Carey gave birth to fraternal twins via C-section in April. She performed for a few hundred people Thursday night at New York's Gotham Hall.
Of her return she said: "I didn't realize this was a big deal."
The concert was one of four shows Thursday dubbed "Plot Your Escape: Four Concerts. Countless Celebrities. 1 Epic Night," by Caesars Entertainment.
Diddy joined Carey in New York, while Lil Wayne and Cee Lo performed in Los Angeles, Maroon 5 and Sara Bareilles in Chicago, and Mary J. Blige and Gavin DeGraw in New Orleans.
