My copy is Skyrim is uptodate.
When I start the game, it runs smooth. I enter a building like Breezehome and everything is fine. As soon as I leave my home, I experience some massive lag. This happens in every building I enter and leave. Sometimes if I fast travel, the problem is fixed...BUT the problem can sometimes occur IF i fast travel. I usually have to exit the game and restart it for it to run smooth again. What might be causing the probem and how can I fix it?

I'm having the same issue. At first I thought it was due to some of the mods I was using, but I deactivate all of them and the issues persisted.

It happens to me only when I enter or exit a building. If I'm inside a building or game world from the start, it runs smoothly, and I can actually go through a few cells before it hits. But then, when I randomly load into a new cell, my FPS plummets to less than 10... Also, I do have autosave on when entering and exiting buildings, if that helps.

I don't want to have to do a clean install, so hopefully someone can help us.

Is anyone else having this issue? Is it related to having too many .esp files?

Try turning off autosave, all of them. See if if still happens. For whatever reason, this fixed it for me.

I do not have autosave enabled in the menu. Is there a way to turn it off in the .ini configuration file?

This happened to me once! I came out of a dwemer dungeon and was greeted with 5 FPS! Alt+Tab to desktop and back fixed it and it hasn't reappeared. I run with all auto-saves enabled BTW.

The "lag" as you call it did increase a bit with the HD texture pack. Exiting a building into the world does take an extra second or two to load depending on where you are in the game. I'm running a 10K RPM Raptor drive and it's quit obvious that it's a data issue. Can someone running an SSD chime in here as to the impact they've seen if any? I would suspect that a 7200 RPM drive or worse, the 5400 RPM drives would be even more noticeable.

I am still having this issue...BAD. I will try alt tabbing to see if that fixes it.

Same lag here. I installed Skyrim a week ago and this lag when leaving a building happens more and more often. On the top of that it also has started happening in buildings/caves. No mods, all drivers updated, win7ultimate etc.. I have tried lowering graphic settings with no luck.

Hardware: i7-920 cpu, asus gtx560, 6 gigs memory, 1 TB hdd.

The new Skyboost that came out yesterday has helped a lot with this issue for me. Try it out.