The word "fuck" and its derivatives are used a total of 246 times.

The actor who portrays "Vincenzo Lipazzi" (Yakavetta's right hand man), Ron Jeremy, is actually an adult film actor/producer.

The door to the porno club says, "Abandon hope all ye who enter," the same words on the sign to Hell in The Divine Comedy by Dante Alighieri.

At the house where the brothers and Rocco battle Il Duce, Defoe, Willem falls to his knees with his arms raised, composing the classical music in the background as he visualizes the actions. This closely resembles Defoe's death scene from Platoon (1986).

When transposed, the first couple letters of Agent Paul Smecker's name change to "Smaul Pecker" (Small Pecker).

Veteran porn actress Jeanna Fine appears as a dancer.

At one point Patrick Swayze, Stephen Dorff, and Robert De Niro were each slated to act in this movie.

The Boondock Saints is also the name of writer/director Troy Duffy's band.