I'm hoping that some of the cat owners here might be able to help.

I took in an abandoned cat 7 months ago. He's been very good about using the litter box. For the past 1 1/2 weeks he's been peeing on my bedroom door and this morning I found a pee stain on one of my bedroom curtains (one of the windows he likes to hang out in.) For "solids" elimination he uses his box. The box hasn't been moved and it's cleaned very often. He appears healthy (eating/drinking well and very active.) Any thoughts/suggestions would be greatly appreciated.