Just moved to Windows 10 instead of Windows 7.
Faced a sudden problem with Baldur's Gate ToS:
The game is running stretched by default when using full screen.
Looks ugly and for me this game is used to be played 4:3.
Didn't find any setting in Windows or GPU driver (GeForce 670 GTX (23.21.13.8813)).
Can someone help me with this issue, please?

Is that The Original Saga? If you're like me and are playing on a laptop with both an Intel GPU and an NVIDIA GPU, then make sure you're running the game with the Intel card. You can change the setting in the Intel HD Graphics Control Panel: Right Click on desktop, Graphic Properties..., Display, select Maintain Aspect Ratio, then Apply.

Hello,
Yes,it's The Original Saga.
But I'm playing on PC with external GPU GeForce 670...

Right click on your desktop to open the Nvidia Control Panel
Under display > Adjust desktop size and position
Scaling Mode Aspect ratio.

See pic.

I got setting exactly like yours, but it keeped stretching.
Finally I switched option "Perform scaling on" from Display to GPU and know it works like it should!
Thank you for help:)