text: Rolando Molina - Hector Sanchez (3 episodes, season 7)
  Tim Monsion - Dr. Cunningham (2 episodes, season 2)
  Felice Heather Monteith - Nurse Marcy (2 episodes, season 3)
  Chloë Grace Moretz - Sheri Maltby (2 episodes, season 3)
  Betty Murphy - Alberta Fromme (5 episodes, seasons 1-3)
  Harry S. Murphy - Mr. Lentz (3 episodes, seasons 1-2)
  N
  Bob Newhart - Morty Flickman (3 episodes, seasons 1−2)
  John Haymes Newton - Jonathan Lithgow (2 episodes, season 1)
  O
  Conor O'Farrell - Detective Copeland (3 episodes, season 1)
  Gail O'Grady - Anne Schilling (4 episodes, season 5)
  Shannon O'Hurley - Mrs. Truesdale (2 episodes, seasons 1-2)
  Peter Onorati - Warren Schilling (2 episodes, season 5)
  Lupe Ontiveros - Juanita "Mama" Solis (8 episodes, seasons 1 and 8)
  Ion Overman - Maria Scott (3 episodes, season 5)
  P
  Sam Page - Sam Allen (7 episodes, season 6)
  Dougald Park - Xiao-Mei's doctor (3 episodes, seasons 2-3)
  Andrea Parker - Jane Carlson (11 episodes, season 8)
  Adrian Pasdar - David Bradley (3 episodes, season 2)
  Alejandro Patino - Ralph (5 episodes, season 2)
  Sarah Paulson - Lydia Lindquist (2 episodes, season 4, 8)
  Tony Plana - Alejandro Perez (5 episodes, seasons 7-8)
  Q