I actually think there is very little correlation. For some there probably is, by coincidence, or some other factors...but there are countless cases where people did very well on their MCAT and struggle through med school. MCAT, USMLE, etc. test only one thing: how hard you are willing to study for an exam. There are people out there who have different work ethics, and put more value on different things in life. For example, I was above the mean on all second year exams, but by third and fourth I was tired of putting so much emphasis on my school work and so little on my life, so I began to study much less and put more into enjoying life. Your grades go down, but who cares? I also know some people who did marginal, at best, on the MCAT and did pretty darn well in med school. The MCAT exists so they can have another factor to use in weeding out applicants. You will see that there are tons of doctors you will work with who rocked on their standardized exams, and are not the best clinicians. I know some attendings who have laid-back dispositions, and saw no reason to kill themselves in med school, and did so-so, and are the greatest physicians. The bottom line is that humans have still not figured out any good way/method of measuring or determining another human's intelligence. We have loads of tests that make us feel like we're really measuring something, but we're not. If someone truly is not that intelligent, it is true that he will have difficulty on an exam...however the reverse is certainly not true. People who design these tests will be the first to tell you (in private, of course) that they have absolutely ZERO ability to tell you anything about the person taking it, and that they have absolutely no real idea yet of how to measure knowledge or intelligence. It's like the 7 day rule for antibiotics; why do we require a 7 day course for most, or 10 for some? Look it up...there's absolutely no good reason; the only reason is that we 'need' something to hang our hats on. The answer is that in our world we line up hoops all in a row, and we just have to suck it up and jump through them. Unfortunately you will find throughout your career that there are those who "aced" the hoops bit and are complete dolts.