The mini-clinical evaluation exercise (mini-CEX) is a well-established method of assessing trainees' clinical competence in the workplace. In order to improve the quality of clinical learning, factors that influence the provision of feedback are worthy of further investigation. A retrospective data analysis of documented feedback provided by assessors using the mini-CEX in a busy emergency department (ED) was conducted. The assessors comprised emergency physicians (EPs) and trauma surgeons. The trainees were all postgraduate year one (PGY1) residents. The completion rate and word count for each of three feedback components (positive feedback, suggestions for development, and an agreed action plan) were recorded. Other variables included observation time, feedback time, the format used (paper versus computer-based), the seniority of the assessor, the gender of the assessor and the specialty of the assessor. The components of feedback provided by the assessors and the influence of these contextual and demographic factors were also analyzed. During a 26-month study period, 1101 mini-CEX assessments (from 273 PGY1 residents and 67 assessors) were collected. The overall completion rate for the feedback components was 85.3 % (positive feedback), 54.8 % (suggestions for development), and 29.5 % (agreed action plan). In only 22.9 % of the total mini-CEX assessments were all three aspects of feedback completed, and 7.4 % contained no feedback. In the univariate analysis, the mini-CEX format, the seniority of the assessor and the specialty of the assessor were identified as influencing the completion of all three components of feedback. In the multivariate analysis, only the mini-CEX format and the seniority of the assessor were statistically significant. In a subgroup analysis, the feedback-facilitating effect of the computer-based format was uneven across junior and senior EPs. In addition, feedback provision showed a primacy effect: assessors tended to provide only the first or second feedback components in a busy ED setting. In summary, the authors explored the influence of gender, seniority and specialty on paper and computer-based feedback provision during mini-CEX assessments for PGY1 residency training in a busy ED. It was shown that junior assessors were more likely to provide all three aspects of written feedback in the mini-CEX than were senior assessors. The computer-based format facilitated the completion of feedback among EPs.