Assessment is more educationally effective when learners engage with assessment processes and perceive the feedback received as credible. With the goal of optimizing the educational value of assessment in medical education, we mapped the primary literature to identify factors that may affect a learner's perceptions of the credibility of assessment and assessment-generated feedback (i.e., scores or narrative comments). For this scoping review, search strategies were developed and executed in five databases. Eligible articles were primary research studies with medical learners (i.e., medical students to post-graduate fellows) as the focal population, discussed assessment of individual learners, and reported on perceived credibility in the context of assessment or assessment-generated feedback. We identified 4705 articles published between 2000 and November 16, 2020. Abstracts were screened by two reviewers; disagreements were adjudicated by a third reviewer. Full-text review resulted in 80 articles included in this synthesis. We identified three sets of intertwined factors that affect learners' perceived credibility of assessment and assessment-generated feedback: (i) elements of an assessment process, (ii) learners' level of training, and (iii) context of medical education. Medical learners make judgments regarding the credibility of assessments and assessment-generated feedback, which are influenced by a variety of individual, process, and contextual factors. Judgments of credibility appear to influence what information will or will not be used to improve later performance. For assessment to be educationally valuable, design and use of assessment-generated feedback should consider how learners interpret, use, or discount assessment-generated feedback.