Do the Percy Jackson and the Olympians books have to be read in order?

I strongly suggest this; because things that happen or are said in one of the early books come around again in the next, and even the last one. It may or may not make sense to you reading them in a random order, but trust me; it'd be best to read them in the correct order; The Lightning Thief, The Sea of Monsters, The Titans Curse, The Battle of the Labyrinth, The Last Olympian, and The Lost Hero. Have fun!