Greater Wolfweres are significantly stronger version of Wolfweres.
In Baldur's Gate: Tales of the Sword Coast Edit
Greater wolfweres are the bosses of Lycanthrope Island and, as such, are much stronger than the ones encountered in Baldur's Gate 2. The most distinguishing feature of greater wolfweres is that they can only be harmed by silver weapons and magic. They also have extremely high HP regeneration - 5/second, or 30 HP per round. Fortunately, their actual maximum HP is relatively low, at 66. Therefore, to kill a greater wolfwere, one must concentrate the attacks of the entire party on a single opponent, and finish them off as quickly as possible.
The only weapons in the game with the silver attribute are:
Backstabbing with Werebane is very effective and can sometimes one-shot them.
While greater wolfweres have no magic resistance, they have 50% elemental resistance, so the best spells to use are ones that do pure magic damage such as Magic Missile or Skull Trap. Various disabling spells (Blind, Hold, Slow, Wand of Paralyzation, Rigid Thinking, etc.) will also work, though the greater wolfweres have saves in the 5-7 range.
In Baldur's Gate 2 Edit
While silver weapons still work, greater wolfweres can also be damaged with any weapon with an enchantment of +3 or higher, and their HP regeneration was toned down to 5/round.