William Peter Blatty Director George C. Scott Kinderman Actor Ed Flanders Father Dyer Actor Brad Dourif The Gemini Killer Actor Jason Miller Patient X Actor Nicol Williamson Father Morning Actor Scott Wilson Dr. Temple Actor Nancy Fish Nurse Allerton Actor George Di Cenzo Stedman Actor Viveca Lindfors Nurse X Actor Carter DeHaven Producer James G. Robinson Executive Producer Joe Roth Executive Producer Gerry Fisher Cinematographer Todd C. Ramsay Film Editor Peter Lee-Thompson Film Editing Barry De Vorzon Original Music Leslie Dilley Production Design Robert C. Goldstein Art Director Henry Shaffer Art Director Hugh Scaife Set Decoration Dana Lyman Costume Design Sally Dennison Casting Julie Selzer Casting Louis DiGiaimo Casting