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