The 29-year-old has been a supporters' favorite at Welford Road since his arrival five years ago from Calvisano and is just one match away from reaching 50 Heineken Cup appearances.
"A player has to think about a lot of things when he is trying to decide on the future," said Castrogiovanni.
"Money is not everything. I always said I enjoy my rugby at Leicester, I like it here and I always had in my mind that I wanted to stay.
"The club and the players have been great for me and I am very happy here. The supporters have been brilliant too.
"The support they have shown me, especially recently, has been unbelievable and I thank them for that."
Director of rugby Richard Cockerill, who saw his side clinch a place in the knock-
out stages of the Heineken Cup at the weekend, was full of praise of the hard working prop.
"Castro has had opportunities to go elsewhere, but he has shown his commitment to Tigers," he said.
"He is a world-class player and we are delighted he has agreed to stay."