Most patches don't change anything that would affect FPS.

Try starting with this guide, http://na.leagueoflegends.com/board/...php?p=24115467

And if you're still having issues, please come back with an attached DxDiag file.

Repair

Aregionius you happen to keep stating this in many posts. However, it seems very unlikely that every person posting about FPS issues or latency issues has problems with their computers and drivers. I have been searching this forum repeatedly for weeks and there are hundreds of pages of posts regarding this issue, most of which you post your FPS guide and state patches do not contain code that would effect FPS. Just because they may not affect FPS directly if this many people are having this issue wouldn't it be almost conclusive that something else is going on behind the scenes, maybe network or service issues? Im not calling you out but it seems highly unlikely every person posting about these issues has driver and computer issues. It can possibly be Riot's fault and not the actual audience that plays the game.

im having this issue too, i start the game at my usual settings and it well eventually drop to 40 for a couple mins then go back to 60. after about 40 mins it drops to ~20 and stays there and starts to lag my entire computer. i fixed it once a while ago by re installing the game but after 3 times it still is happening