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