<p>Medical mistakes made while in a state of cognitive fatigue result in diagnostic errors, psychological distress, poor patient outcomes, and potentially, loss of life. To date, cognitive fatigue in health professionals is assessed via self-report; however, the reliability and validity of these measures are often challenged. Here we propose the use of mobile electroencephalography (mEEG) in a medical context as an objective cognitive fatigue assessment that is cost effective, reliable, and efficient. We had medical students complete a simulated night on call during which they diagnosed a series of simulated medical cases. Before and after their shift, we assessed cognitive fatigue using both behavioural and mEEG measures. Our results demonstrate a decrease in the amplitude of a neural response sensitive to cognitive fatigue from the start to the end of the simulated night on call — a finding associated with an increase in cognitive fatigue. Interestingly, we observed no reltionship between the neural response and subjective self-reported cognitive fatigue scores, supporting the need for objective as opposed to subjective measures when asasessing cognitive fatigue.</p>