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