BACKGROUND: Clinical simulation has become widespread as a training and assessment tool across a range of health professions, including emergency care. As with any form of assessment, simulations may be associated with stress and anxiety ("distress") which may have a negative effect on student performance if demands required by the simulation outweigh the available resources. This study aimed to assess the effect of participation by students in an emergency care simulation on an objective measure of stress and a subjective measure of anxiety. METHODS: Heart rate variability (HRV) and scores from a validated state anxiety instrument (the State-Trait Anxiety Inventory) were assessed in 36 emergency medical care students participating in scheduled simulation assessments. Data recorded during a resting control period were used for comparison. RESULTS: HRV variables showed changes in the simulation assessment group suggesting decreased variability and parasympathetic withdrawal, however these were not significantly different to control. Heart rate in the simulation assessment group increased significantly (73.5/min vs. 107.3/min, p < 0.001). State anxiety scores increased significantly both before (33.5 vs. 49.1, p < 0.001) and after (33.5 vs. 60, p < 0.001) the simulation assessment, compared to control. No linear relationship was found between any HRV variables and anxiety scores. CONCLUSION: Participating in an emergency care simulation assessment significantly elevated levels of anxiety in a group of 36 students, however an objective measure of stress did not identify changes significantly different to those at rest, with the exception of heart rate. The high levels of anxiety documented before and after simulation assessments may have a negative effect on performance and require further investigation.