Yes. I originally bought SIDIs that were more or less in my usual size (I say more or less because they use European sizing). I found them to be a little tight come summer, so I bought another pair in a size bigger. I like the bigger size for winter use, too, because I can wear a slightly thicker wool sock without losing circulation.

Regardless of size, however, the shoe has to otherwise fit me in the heel. SIDIs are the only road shoe I've found that are tight enough in the heel so as not to slip on my foot. I also run a stiffer insole (SOLE is my insole of choice) in them than the standard-issue SIDI insole. It takes a wee bit of extra room.