Here is the full list of all 37 Psychonauts achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Complete Meat Circus.
Achieve Rank 101.
Sort all Emotional Baggage.
Gather all Figments.
Crack all Vaults.
Revisit all brains after completion.
Complete The Asylum.
Introduce all Camp Kids to Mr. Pokeylope.
Re-brain the Children.
Complete Black Velvetopia.
Find all Golden Helmets.
Find Edgar's Secret Garden.
Complete Waterloo World.
See yourself through the eyes of many others.
Redeem all 16 Scavenger Hunt Items.
Complete Gloria’s Theater.
Complete The Milkman Conspiracy.
Complete Lungfishopolis.
Complete the Punchy Target mini-game.
Hear Vernon's Ghost Story.
Spy on Bobby's love life.
Complete Milla’s Dance Party.
Uncover Milla's Secret.
Use the bacon. A lot.
Discover the secret history of Whispering Rock.
Give the Coach's speech on the stump.
Complete Sasha’s Shooting Gallery.
Cook and consume two different kinds of roast in one sitting.
Witness Maloof's transformation.
Buy an item from the Camp Store on Christmas.
Read many bulletin board messages.
Complete Basic Braining.
Achieve Rank 40.
Achieve Rank 60.
Achieve Rank 80.
Earn all Merit Badges.
Achieve Rank 20.