@stacysclass - the answer to your question is yes, yes, yes! Urinating outside the box, not just missing, was the first clue I got that something was wrong with my kitty. I took her to the vet and found out she had diabetes (OTJ now!). She did not have a UTI and she was not avoiding the litter box completely, she was using the box and peeing outside the box. I could not find any info on exactly what to do in order to correct it so i did a little bit of everything.
It took some hard work but we have resolved the peeing issue completely at my house. Here are the steps I took that worked for me:
1. You MUST find all areas where (s)he has been peeing outside the box. I bought a black light and creeped around my house like an insane person and marked all the areas with painter's tape
2. Once you find the areas, clean them thoroughly with an enzyme cleaner
3. While the areas are wet, cover them in tin foil. I didn't notice at first but if you read the fine print on the enzyme cleaner, it does not neutralize the smell until it dries. So if you put tin foil in the area, it usually deters the kitty from walking on it (learned this from Jackson Galaxy) while it dries and becomes effective
4. More litter boxes. I have 3 litter boxes for one kitty. She is very snooty about using a dirty litter box
5. Scoop every day, scrub every other week. I scoop her litter boxes several times a day (usually before and after work) and then scrub them clean every other week
6. Feliway - I put a plug in Feliway diffuser in the room where two of her litter boxes are (this room is carpeted so was my main concern, the other litterbox is on tile)
Also, my kitty has elevator butt and tends to begin standing while still peeing. This causes her to pee outside the box on accident. I have managed to correct this behavior by taping a trashbag over 1/3 of the litterbox in the back. She gets in the box to pee and while she lifts up, her bum stays under the trash bag so she doesn't spray outside the box.
I know it sounds like a lot of work and i'm not sure if she would have stopped if I had only done one of those steps instead of all of them but this has worked for me (knock on wood) and we have not had an incident since January. She is also in remission so i'm sure that helps as well.