A list of the Halloween costumes the main characters have worn through the years.
- 1997 – Salt (Marshall) & Pepper (Lily) and Cumin (Ted) - The Stinson Missile Crisis
- 1998 – Lady (Lily) & the Tramp (Marshall) and their bowl of spaghetti (Ted) - The Stinson Missile Crisis
- 2000 – Lewis (Lily) & Clark (Marshall) and their canoe (Ted) - The Stinson Missile Crisis
- 2001 – Hanging chad (Ted), Sonny (Lily) & Cher (Marshall) - Slutty Pumpkin
- 2005 – Jack Sparrow (Marshall), parrot (Lily), Top Gun/Devil/Penguin (Barney), Hanging chad (Ted) - Slutty Pumpkin
- 2006 – Dr. Frankenstein (Lily) and his monster (Marshall) and a scared villager (Ted) - The Stinson Missile Crisis
- 2007 – C3PO (Marshall), R2D2 (Lily) and the robot Luke's Uncle almost bought from the Jawas (Ted) - The Stinson Missile Crisis
- 2007 – Present (Marshall), thank you note (Ted) - The Poker Game
- 2010 – Hot dog (Ted), Johnny Lawrence from The Karate Kid (Barney), bull (Marshall), matador (Lily) - Canning Randy
- 2011 – Mountie/Apollo Creed (Barney), hockey player (Robin), Hanging chad (Ted) - The Slutty Pumpkin Returns
- 2016 – Ahab (Marshall), Whale (Lily), Hanging chad (Ted), 2000 voter (Tracy), David Lee Roth (Barney), no costume because she was too busy (Robin) - Last Forever - Part One
- 2020+ - Ted says Robin's a big fan of Halloween, always dressed up in costumes (Slutty Pumpkin), so she probably dresses for Ted's and Marshall and Lily's kids.
Additional Notes -
- It's likely that Professor Ted wore the hot dog costume for his class in 2010, but wore the hanging chad costume in the evening for the rooftop party in the hopes of running into the Slutty Pumpkin (Naomi).
- Apparently Ted was insistent on wearing the thank you note costume to the roof top party in 2007 even though he also wore the robot that Luke's uncle almost bought the same year. Ditto Marshall's Present and C3PO costumes.
- It's interesting to note that if Ted had worn the hanging chad costume in 2007 instead of the thank you note and wasn't so obsessed he would have run into the Slutty Pumpkin a year earlier since she was at that party wearing the slutty pumpkin costume again.
- Rumors that Lily wore a ghost costume in 1998 and Joan of Arc in 2000 have been verified as false.