The zoo made the announcement on Twitter Wednesday, congratulating mom Lincecum and dad Robin Williams.
The baby has yet to be named but no matter what it's called, you're going to know it when you hear it.
Howler monkeys are among the loudest animals on Earth. Their howl can travel for three miles in a dense forest.
We have a baby howler monkey! Congrats to mom Lincecum and dad @RobinWilliams! @timlincecum Photo by Marianne Hale pic.twitter.com/H6zRasPCmo
— San Francisco Zoo (@sfzoo) March 18, 2015