Robert Duvall as THX

Donald Pleasence as SEN

Don Pedro Colley as SRT

Maggie McOmie as LUH

Ian Wolfe as PTO

Marshall Efron as TWA

Sid Haig as NCH

John Pearce as DWY

Irene Cagen as IMM

Gary Alan Marsh as CAM

John Seaton as OUE

Eugene I. Stillman as JOT

Jack Walsh as TRG

Mark Lawhead as Shell Dweller

Robert Feero as Chrome Robot

Johnny Weissmuller Jr. as Chrome Robot

Claudette Bessing as ELC

Susan Stroh as Control Officer

James Wheaton as OMM (voice)

Henry Jacobs as Mark 8 Student

Bill Love as Mark 8 Instructor

Doc Scortt as Monk

Gary Austin as Man in Yellow

Scott L. Menges as Child #1

Toby L. Stearns as Child #2

Paul K. Haje as Trial Prosecutor

Ralph Chesse as Trial Proctor

Dion M. Chesse as Trial Defender

Bruce Chesse as Trial Pontifex

Mello Alexandria as Hologram Dancer

Brandyn Barbara Artis as Hologram Dancer

Morris D. Erby as Hologram Newscaster

Willie C. Barnes as Hologram Comic

Richard Quinnell as Hologram Comic

Jean M. Durand as Hologram Listener

Scott Beach as Announcer (voice)

Neva Beach as Announcer (voice)

Terence McGovern as Announcer (voice)

Julie Payne as Announcer (voice)

James Cranna as Announcer (voice)

Ruth Silveira as Announcer (voice)

Bruce Mackey as Announcer (voice)

David Ogden Stiers as Announcer (voice)

Bart Patton as Announcer (voice)