The Clinical Skills Assessment is an OSCE-based performance examination that is now the final test requirement for Educational Commission for Foreign Medical Graduates certification of graduates of foreign medical schools. Its design, test development and scoring methodologies are presented, as are the processes used for validation, standard setting, calibration and equating. Some of the logistical challenges of implementing a high-stakes examination for a population of uncertain size and potentially high heterogeneity are considered. Finally, the unique aspects of Clinical Skills Assessment in comparison with other OSCE instruments are highlighted.