From a human viewpoint, nothing has changed. From a feline view, SOMETHING IS WRONG! The tough part is figuring out WHAT.

As already mentioned, first step would be to rule out a UTI. Although usually, they don't "go" in the same place over and over with a UTI. Still, see if you can take in a sample for testing.

Things that may have changed, run from the obvious to the "you have GOT to be kidding!"

- litter: brand, type, scent
- box: placement, frequency of cleaning
- food or water bowl placement (yes, if kitty decides it it soo close to the litter box, he won't use the box!)
- started running central a/c -- you'd be surprised how the smells flow around the room differently!
- new family member; room mate; guests for the holiday INCLUDING any pets which may have arrived
- painted, varnished, etc. near the box but not across the room

You did not mention which room his box is in. Any changes in that room may have disrupted him.

Is he an only cat? Has another cat decided not to allow him in the box?

When all else fails, to keep your sanity add a second box where he is now going and see if he takes to it. Yes, this means "cat wins," but really, do you want to struggle if all he wants is a new bathroom in a new location?

Good luck! I've been through it when it was not a physical problem, makes me nutty!