Sorry, I can't reproduce this. In my tests, surgery works just like it's supposed to.
If you could provide me with a savegame right before a battle where it doesn't work for you, that might be helpful.

Thanks for your reply.
I can’t do that because I play with the selected option “no quitting without saving”.
Do you have any suggestions why the surgery skill is not working properly? Maybe I did something wrong in the TLD options?

Little I can do for you if you choose unrecommended settings.
Anyway, you can still tab out in a battle where it happens, and back up your savegame.
I doubt there's much you can do, other than performing a clean reinstall if you haven't already.

Thanks for your recommendation. I’ll leave a message in this discussion if I can fix this problem.

You can still just send me your current savegame, maybe it helps me replicate the problem.

Also, in order to rule out a few global variants that might interfere: Did you fight the battle alone, join a battle, or were joined by allies? Did you die during the battle?
The casualties you reported were all in your party, I assume?

I see you edited your first post. The base chance is calculated differently in TLD, but that shouldn't be the problem here.

1.) For some reason, Steam doesn't allow me to send my savegame.
2.) Yes, we've fought one army against another, no one came to help me or him. I wasn't wounded during the battle, just like my surgeon (Fanuil). Yes, the indicated casualties are only from my army.
3.) Thank you for the information, it's good to know.