Manga Bits
Created by Kentarou Miura, Berserk made its 1989 debut in Young Animal magazine. It's currently serialized in the mag, with 26+ manga volumes [tankoubon] under the Young Animal/Jet Comics label.
Besides having enthralling storylines, the manga is very graphic. Berserk depicts everything from extreme violence, rape and incest. So its for a mature audience.
In 2003, Dark Horse's manga division picked up license to publish the US english release of Berserk. Currently available ^.^
Anime Bits
Berserk is also an intense 25-episode anime series based on manga volumes 1-13. It originally aired in Japan about 1997 with a late-night time slot. The anime ended on its own accord, since the manga is ongoing. Berserk parted in a way that could be revisited ^.^
In 2002, Anime Works, a division of Media Blasters, released the complete US DVD edition. Currently available in six volumes.