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