To probe medical students' narrative essays as a rich source of data on the hidden curriculum, a powerful influence shaping the values, roles, and identity of medical trainees. In 2008, the authors used grounded theory to conduct a thematic analysis of third-year Harvard Medical School students' reflection papers on the hidden curriculum. Four overarching concepts were apparent in almost all of the papers: medicine as culture (with distinct subcultures, rules, vocabulary, and customs); the importance of haphazard interactions to learning; role modeling; and the tension between real medicine and prior idealized notions. The authors identified nine discrete "core themes" and coded each paper with up to four core themes based on predominant content. Of the 30 students (91% of essay writers, 20% of class) who consented to the study, 50% focused on power-hierarchy issues in training and patient care; 30% described patient dehumanization; 27%, respectively, detailed some "hidden assessment" of their performance, discussed the suppression of normal emotional responses, mentioned struggling with the limits of medicine, and recognized personal emerging accountability in their medical training; 23% wrote about the elusive search for personal/professional balance and contemplated the sense of "faking it" as a young doctor; and 20% relayed experiences derived from the positive power of human connection. Students' reflections on the hidden curriculum are a rich resource for gaining a deeper understanding of how the hidden curriculum shapes medical trainees. Ultimately, medical educators may use these results to inform, revise, and humanize clinical medical education.