Here is the process if you already have a subspecialty in Germany:
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#1 register with the ECFMG (
www.ecfmg.org)
#2 get application materials to participate in the US medical licensing exam (
www.usmle.org)
#3 apply for admission to the exam providing various documents such as your medical school diploma
#4 take USMLE step1 (can be done in germany)
#5 take USMLE step2ck (can be done in germany)
#6 come to the US, take USMLE step2cs (a practical exam)
#7 Then you have to find a residency program. Look for the 'FREIDA' database on the american medical association website. Check out
www.nrmp.org to find information about the centralized process to obtain a residency position.
#8 You have to obtain a visa to be allowed to train here. Either a J1 (exchange visitor) or H1b (temporary specialty worker) visa.
#9 Do your residency training.
#10 After 2-3 years of residency training in the US, you are eligible to obtain a full unrestricted medical license. The medical license is issued by the medical board of the individual state. You can find a list of individual states medical boards at the website of the federation of state medical boards.
www.fsmb.org Different states have different rules, but most require pretty much the same stuff: 2-3 years of US residency training, USMLE 1-3 and a valid ECFMG certificate.
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In case you wondered. Yes, it is exactly the same process as if you are fresh out of medschool. The US for the most part doesn't accept postgraduate training done outside of the US and canada. You might have a leg up in looking for a residency, but typically you have to repeat your entire postgraduate training.
The only exception is academic practice. If you have a strong research background and a US medical school hires you on a tenure-track position, you might be able to practice your specialty without having to go through residency again (and depending on the state, sometimes without having to write the USMLE). However, the way from these academic positions into the private practice market is very difficult.