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