Monitoring one's learning activities is a key component of self-regulated learning (SRL) leading to successful learning and performance outcomes across settings. Achievement emotions also play an important part in SRL and consequently student learning outcomes. However, there is little research on how specific types of monitoring (i.e. Feeling-of-Knowing, Judgement-of-Learning) and achievement emotions jointly affect performance in clinical reasoning within computer simulated environments. In this study, we explored the joint predictive value of monitoring judgements and achievement emotions in medical students' ability to make accurate and efficient clinical diagnoses using BioWorld, a computer-based learning environment designed to help medical students practice clinical reasoning skills. Multiple types of data (log files, verbal protocols, self-report questionnaires) from 27 students were analyzed using text mining and linear mixed-effects models. We found that feeling-of-knowing judgements positively predicted diagnostic efficiency whereas judgement-of-learning and the achievement emotion of anger negatively predicted diagnostic efficiency. Achievement emotion of pride positively predicted confidence in diagnosing the case correctly. This study not only provides theoretical and methodological insights but also alert medical instructors to the many dimensions of diagnostic performances and effective intervention strategies in clinical reasoning.