The aim of this study was to use medical students' critical incident narratives to deepen understanding of the informal and hidden curricula. The authors conducted a thematic analysis of 272 stories of events recorded by 135 third-year medical students that "taught them something about professionalism and professional values." Students wrote these narratives in a "professionalism journal" during their internal medicine clerkships at Indiana University School of Medicine, June through November 2007. The majority of students' recorded experiences involved witnessing positive embodiment of professional values, rather than breaches. Attending physicians and residents were the central figures in the incidents. Analyses revealed two main thematic categories. The first focused on medical-clinical interactions, especially on persons who were role models interacting with patients, families, coworkers, and colleagues. The second focused on events in the teaching-and-learning environment, particularly on students' experiences as learners in the clinical setting. The findings strongly suggest that students' reflective narratives are a rich source of information about the elements of both the informal and hidden curricula, in which medical students learn to become physicians. Experiences with both positive and negative behaviors shaped the students' perceptions of the profession and its values. In particular, interactions that manifest respect and other qualities of good communication with patients, families, and colleagues taught powerfully.