Work stress in doctors is an issue for the doctors themselves, their patients, and healthcare organisations as a whole. Previous research indicates that work stress is a cause for concern in trainee doctors in particular. While their stress has been largely attributed to organisational factors such as long working hours, a demanding workload and changeable work conditions, the specifics of when and why stress occurs, how it is experienced and its impact has not been thoroughly investigated. Recent advances in methods of tracking ambulatory changes in work activity, behaviour and physiological functioning make it possible to study correlates of stress as they occur. The studies presented in this PhD thesis use advanced technologies and methodologies with the aim of providing new information to quantify the working day of a trainee doctor and investigate in real time the possible determinants, correlates and patient safety relevant consequences of their stress. The PhD contributes methodologically by investigating the validity of standard measures of workplace stress, and by documenting and evaluating a complex real time protocol to measure workplace stress in doctors. Results from the main empirical study reported in this thesis reveal what a typical working day entails for doctors in their first postgraduate year. The tasks and situational factors they are most likely to find stressful are discussed in detail, as are the performance-related consequences of their stress. Based on these results, suggestions have been made for future research and practice, with implications for medical training and the development of future interventions to alleviate stress in trainee doctors.