OBJECTIVES: The formative aspect of the mini-clinical evaluation exercise (mini-CEX) in postgraduate medical workplace-based assessment is intended to afford opportunities for active learning. Yet, there is little understanding of the perceived relationship between the mini-CEX and how trainees self-regulate their learning. Our objective was to explore trainees' perceptions of their mini-CEX experiences from a learning perspective, using Zimmerman's self-regulated learning theoretical framework as an interpretive lens. DESIGN: Qualitative, using semi-structured interviews conducted in 2017. The interviews were analysed thematically. SETTING: Geriatric medicine training. PARTICIPANTS: Purposive sampling was employed to recruit geriatric medicine trainees in Melbourne, Australia. Twelve advanced trainees participated in the interviews. RESULTS: Four themes were found with a cyclical inter-relationship between three of these themes: namely, goal setting, task translation and perceived outcome. These themes reflect the phases of the self-regulated learning framework. Each phase was influenced by the fourth theme, supervisor co-regulation. Goal setting had motivational properties that had significant impact on the later phases of the cycle. A 'tick box' goal aligned with an opportunistic approach and poorer perceived educational outcomes. Participants reported that external feedback following assessment was critical for their self-evaluation, affective responses and perceived outcomes. CONCLUSIONS: Trainees perceived the performance of a mini-CEX as a complex, inter-related cyclical process, influenced at all stages by the supervisor. Based on our trainee perspectives of the mini-CEX, we conclude that supervisor engagement is essential to support trainees to individually regulate their learning in the clinical environment.