My recollection is that there were more med-psych programs and then the fp/psych started to pop up after that. As for geographic location - my own guess is it has a lot to do with the quality of the FP programs. I know FP is a more desirable field in California relative to a lot of the rest of the country - mostly because primary care and managed care are more popular there. I know that in Chicago, FP was viewed as a less desirable field, but was gaining popularity because of the big push for primary care a few years back. I'm guessing a lot of that interest has disappeared.

At University of Iowa, they actually have both a combined med-psych and an FP-psych program. The med-psych program had been around quite a while, and the FP-psych started up while I was there - I'm guessing around 1998 or so.

I'm guessing each person has their own reasons for choosing to do one of the other - the training is clearly different. My own sense is that an FP residency will have considerably less inpatient medicine exposure, but more outpatient medicine, and obviously you'd also see the OB and peds that int medicine doesn't. I would expect there are probably many people interested in fp-psych who are also interested in med-psych and vice versa.