I'm playing with most of the mods listed in the first post of the "Baldur's Gate 2 essential mods" thread.

Just created an elf f/m/t with 17 con. He has 18 hit points at level 1. I have not summoned a familiar...no idea what is going on. Anyone else have a problem like this?

edit: I'm guessing it might be something in the tweak pack, not sure though.

Are you playing BG 2? If so, you shouldn't be starting off at level 1, so having that much HP doesn't sound horribly wrong, since you get an average of the hit dice of all your classes when you level up.

I am playing with a mod called Baldur's Gate Trilogy which combines all games in the series into one long play experience using the BG2 engine.

The hit points are definitely wrong. For lvl 1/1/1 f/m/t with 17 con hit points should be

(10+3)/3 = 4
(6+3)/3 = 3
(4+3)/3 = 2

for a total of 9 hit points.

Yeah, that sounds like a bug.

I know of a bug that can cause this with rangers, when you go back and forth a bunch of times during character creation while selecting favoured enemies. Perhaps there's a similar bug with the fighter-mage-thief somewhere? Perhaps you went back and forth a bunch of times when selecting weapon proficiencies or spells?

I've never encountered this bug though, nor do I play with the BG trilogy mod, so I can't say for sure what caused it.

Solving it, however, should be easy: use the Shadowkeeper character editor utility to edit your savegame and reduce your hitpoints to the normal level. I think it's compatible with this mod. It's a great utility, and a good idea to have anyway when playing a modded game. Sooner or later something is going to break down, and Shadowkeeper can often fix it.