BACKGROUND: To ascertain if undergraduate medical students attain adequate knowledge to practice in paediatrics, we designed the minimum accepted competency (MAC) examination. This was a set of MCQ's designed to test the most basic, 'must know' knowledge as determined by non-faculty paediatric clinicians. Only two-thirds of undergraduate students passed this exam, despite 96% of the same cohort passing their official university paediatric examination. We aim to describe the psychometric properties of the MAC examination to explore why there was a difference in student performance between these two assessments which should, in theory, be testing the same subject area. We will also investigate if the MAC examination is a potentially reliable method of assessing undergraduate knowledge. METHODS: The MAC examination was sat by three groups of undergraduate medical students and paediatric trainee doctors. Test item analysis was performed using facility index, discrimination index and Cronbach's alpha. RESULTS: Test item difficulty on the MAC between each group was positively correlated. Correlation of item difficulty with the standard set for each item showed a statistically significant positive relationship. However, for 10 of the items, the mean score achieved by the candidates did not even reach two standard deviations below the standard set by the faculty. Medical students outperformed the trainee doctors on three items. 18 of 30 items achieved a discrimination index > 0.2. Cronbach's alpha ranged from 0.22-0.59. CONCLUSION: Despite faculty correctly judging that this would be a difficult paper for the candidates, there were a significant number of items on which students performed particularly badly. It is possible that the clinical emphasis in these non-faculty derived questions was juxtaposed with the factual recall often required for university examinations. The MAC examination highlights the difference in the level of knowledge expected of a junior doctor starting work in paediatrics between faculty and non-faculty clinicians and can identify gaps between the current curriculum and the 'hidden curriculum' required for real world clinical practice. The faculty comprises physicians in employment by the University whose role it is to design the paediatric curriculum and deliver teaching to undergraduate students. Non-faculty clinicians are paediatric physicians who work soley as clinicians with no affiliation to an educational institution. The concept of a MAC examination to test basic medical knowledge is feasible and the study presented is an encouraging first step towards this method of assessment.