Despite the importance and ubiquity of the diagnostic process, diagnostic errors are common and costly, with respect to both health care spending and patient morbidity and mortality. An estimated 10% to 15% of inpatient diagnoses and 5% of outpatient encounters involve diagnostic error, defined as a missed, delayed, or incorrect diagnosis. Diagnostic errors also have a marked impact on health care providers, and the emotional effects of diagnostic error can be long-lasting and harmful. Medical educators then have a duty to address diagnostic errors as part of their quality improvement and patient safety curricula. Given these challenges and the existing educational gap, we created a curriculum in diagnostic reasoning and diagnostic error. This educational activity provides a robust introduction to the topic as well as an opportunity for structured self-reflection about learners’ own experience with diagnostic errors. The educational outcomes were developed not only to give learners the knowledge and skills they need to improve the diagnostic process and decrease diagnostic error but also to cultivate and demonstrate attitudes of humility and openness about diagnostic reasoning and error for learners and faculty. This educational activity was well received by learners and can serve as an introduction for a larger curriculum or as a stand-alone educational activity. It was effective at improving learner knowledge about medical decision-making and cognitive biases and is an important contribution to implementing focused educational interventions about diagnostic error and medical decision-making.