We conducted a study to determine the number of items and successful response rate to questions specific to emergency medicine on the National Board of Medical Examiners Test, Part II (NBME-II). The 1979 and 1983 NBME-II examinations were reviewed by a subcommittee of the Society of Teachers of Emergency Medicine. Items pertaining directly to the core content knowledge base were selected and classified by core content topic and NBME subspecialty. Overall, 14.7% of the 892 items on the 1983 examination pertained to emergency medicine. The successful response rate was 73.3% for the emergency medicine questions. When looked at by sub-specialty categories, the percentage of items pertaining to emergency medicine varied from 1.3% in obstetrics/gynecology to 27.2% of the items in surgery. On the 1979 examination, 13.8% of the questions pertained to emergency medicine, with a successful response rate of 67.1%. Analysis of the data by core content topic showed that some areas (orientation to emergency medicine, ophthalmologic diseases, environmental emergencies, and behavioral emergencies) had two items or fewer on both examinations. Other topics, such as trauma, showed a consistent pattern of questions on both examinations. Our study emphasizes the difficulty of attempting to test competency in the clinical knowledge base of medicine within the artificiality of knowledge base departmental boundaries.