Purpose: In-service exams are a commonly used educational tool in postgraduate medical education. Although most specialties utilize such an exam, medical genetics did not. It was decided in the spring of 2009 at the inaugural Medical Genetics Residency Program Directors (PDs) Group meeting to develop and implement such a test. Methods: Using questions sent in from PDs, a 125-question exam was created, with 125 multiple-choice questions according to the format of the National Board of Medical Examiners. The exam covered genetics in the following areas: basic/molecular (∼45 questions), cancer and adult (20), prenatal (20), biochemical (20), pediatric/dysmorphology (20). The exam was administered for the first time in February 2010, and again with modifications in 2011. Results: In total, 174 trainees from 35 programs completed the exam in 2010; in 2011 the number increased to 214, representing 39 US programs, and 4 Canadian programs. For both years, most participants were medical genetics residents (106 in 2010; 127 in 2011), but a substantial number of clinical laboratory fellows also participated (68 in 2010; 85 in 2011). Conclusion: The development and implementation of this test were an overall success, in that in two years we were able to secure almost 100% participation from medical genetics residency programs, and that we created an infrastructure to develop and implement this exam on a yearly basis. There is need for improvement, notably in the relatively low mean score and relatively narrow spread of scores. However, we believe that, with efforts under way to improve the quality of the questions, the in-service exam will become a fundamental tool in medical genetics residency education. ©American College of Medical Genetics and Genomics.