The number of U.S. citizens attending medical schools outside the United States and Canada has increased recently. Because these people tend to return to the United States to practice medicine, it is important to know more about their characteristics and educational experiences. Based on summary data from certifying examinations, U.S. citizens trained abroad do not perform as well as either other international medical graduates (IMGs) or U.S. graduates. Moreover, they are more likely than non-U.S. citizens to be engaged in primary care activities. Changes in the composition of the IMG pool could affect the makeup and quality of the U.S. physician workforce.