There are three main followers in Diablo 3 for the PC, but how many can you have follow you at once?
Well, of the three main followers, you can only have one follow you at a time. If you get a new follower, your other one will return to town and wait for you to recruit them again.
However there are characters that will follow you during certain quests that don’t replace your main follower, so at certain points of the game you can have up to two followers at a time, but only for a limited time.