Dundas, at King and Cross.
If you're coming from the University, take Main St down to Dundas area (it turns into Osler at some point and then back into Main St), go just past King (at which point Main St turns into Cross St) and it will be on your left, kind of hard to see from the road if you're driving but it's very close to the intersection.
If you're taking a bus, then just take any one that goes down that way (you should go past University Plaza at some point, so make sure you take a bus that goes Osler and doesn't make the left to continue onto Main), get off at King & Cross (usually the buses make a left onto King) and then walk up Cross St for about two minutes.
http://cmlhealthcare.com/clinic/?id=1603
That's the info because my directions are from memory so they probably suck