Recessing cabinets involves fitting the back of the cabinet between the framing behind the drywall. If the body portion of the cabinet is small enough to squeeze between studs and your studs are positioned correctly, it's easy. If not (either studs aren't positioned exactly how you want the mirror to line up or the cabinet is too big), you'll have to change the framing to accommodate. I am not a construction expert, but you could essentially frame in a niche or window in the framing for the cabinet to slide into. Depending on whether it is a load bearing wall or not, you may have to make certain the framing properly supports the load (like a window on a load bearing wall might).

Thanks for your thoughts.fori, I think it will overwhelm, my DH doesn't and the salesperson at the bath/plumbing supply company tells me oversized cabinets are the style! It is a 10x10 bathroom, with a 78 inch vanity on one wall. The cabinets are 24x33, 5 1/2 in. deep...just seems way too big to me. I don't need the storage, we're having an antique-style linen closet built for the other wall that will have plenty of storage.
pricklypearcactus, the "window framing" was just what our GC was going to do for our recessed cabinets in the other bathroom! I just wasn't sure if the construction of a wall mount would allow it to be recessed....guess we'll have to go look at them (we're keeping them stored at the supply co. until we're ready for them).

I bought my Restoration Hardware medicine cabinet without realizing it wasn't the right one. SO, I recessed my surface mount cabinet into the bathroom wall, and it was pretty easy. For yours, it sounds like you'll need to reinforce and removed the studs in the wall a bit.

My wall was already set up for the med cabinet I removed, so I just trimmed off the moldings on the cabinet so that the edge of the moldings would act as the 'stop' so that cabinet didn't recess too far in. I hope that makes sense.

I tried it on the wall, but it so overwhelmed my small bathroom and the console sink beneath it, that I went ahead and hacked into it! Now I just need to do some touch up paint....

Anyway, here's a picture of it:

Be careful if you try to recess a surface mount medicine cabinet and it is frameless you might have problems getting the door open. Often, the door is wider than the cabinet and if you fully reces it, it will not be able to open. There are plenty of options for medicine cabinets that do recess.

Here is a link that might be useful: Medicine Cabinets

oldhousegal...When you trimmed the moulding did you trim on all the sides? I am recessing the same cabinet and wondering if I just trim the top and bottom mouldings then fit the un trimmed sides into the wall? Or did you also trim the sides so the sides also acted as a stop?