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