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