There are a number of schools with true P/F for the first two years, among them include:
Harvard
Mount Sinai
USC-Keck (sort of, since technically you can also get dean's recognition at the end of the academic year if you've performed exceptionally well, though this is based on both academic performance as well as "extracurricular" factors)
UCSF
Northwestern
NYU (I think?)
CWRU
Then there seems to be a few schools with true P/F all four years:
UCLA
Stanford
Yale
Pritzker
Among these, only Stanford doesn't have an AOA chapter, so the other schools must still use some form of evaluation to "rank" their students, at least by the end of third year.
Also, some schools have true P/F for the first year only:
Vanderbilt
WashU
Michigan
Duke
The above lists are NOT meant to be comprehensive. I am sure I'm leaving out quite a few. The point is that most schools that use a true P/F system are elite medical schools. The truth is, most medical schools are still using A/B/C/D or H/HP/P/F or H/P/F system. No matter how you call it, these are still very similar grading systems and none of them are P/F in the true spirit of the phrase. Many elite schools still shy away from any true P/F grading, including Hopkins, Emory, UNC, Pitt, Mayo, UCSD, Penn, etc., so there is really no correlation between grading system and how 'highly ranked' a school might be.
Finally, I want to say that don't worry about grading too much. I currently go to a med school without true P/F as listed above, and it's not as bad as I had initially thought. I must admit that I was worried about it last year before entering med school, but having grades really hasn't been overbearing for me. One shouldn't give up a great acceptance just because the school is not true P/F (this is pretty obvious).
NOTE: Current med students at given institutions please correct me if I placed your school in the wrong category above.
