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