I've never been able to get my thief characters to pull off a backstab. The computer seems to be able to do it all the time. How do I do it?

Firstly, ensure your thief is hidden in shadows. Then, position them behind the enemy, and attack. If a hit is scored (at +4 bonus) then the backstab will be successful, so long as the weapon held is usable by a thief character. [EDIT: and a melee weapon, natch]

The behind part is important, and differs from plain BG1 and PS:T, where backstabbing could often seem more akin to "facestabbing", as there was no such distinction. :shake:
Also, enemies don't need to be behind you to land a backstab! :grr:

You can also backstab if you are invisible and behind the enemy.

Things that can prevent backstabbing from being successful include:
- not using a backstabbing weapon (e.g. you can't backstab with a quarterstaff)
- missing your hit roll (thieves have pretty crappy THAC0 so often miss - that's why Fighter / Thieves are best for backstabbing)
- the enemy is immune to backstabbing (e.g. golems, who have no vital organs to stab at)
- you're not hidden properly (e.g. the enemy has True Sight or similar detection spell operating)

Actually, HB is not quite right. Quarterstaffs can be used to backstab. The true issue is that you have to use a weapon that a true-class thief could use. Thus, a mage/thief (or a thief with UAI) could use the staff of the magi, but could not back-stab with it.

Ah, I knew I'd manage to get that one wrong!

Harbourboy may be partially correct. I have a hafling assassin who is proficient with shortsword, and quartrestaff.

I can always pull off backstabb's with any shortsword but I can rarely do this with the 'Staff of Striking'. Can anyone let me know whats wrong?

fighter/thief as multiclass are really the best for backstabing.
With HLA Critical Strike you will Hit and you will do 10 times damage unless its a mage with some protective spells or that creature is immune to backstab.

to DMC: i should try to backstab with staff of ram , thanx for posting this

Hmm, the best HLA for a fighter/thief who wants to do the ole massive damage is the assassination... good main-hand weapon + belm/scarlet ninjato + impr. haste = bad things for the target :)

The Shaman:

- when i have HLA there is no need to cast impr.haste, whirlwind is more then good
- best combination for multi fighter/thief is hide (with spell or skill) , HLA Critical Strike and backstab. That kills anything with one single blow (of course when that creature can be backstabed and wears no helmet)