Healthcare professionals use the genre of case presentation to communicate among themselves the salient patient information during treatment and management. In case presentation, many uncertainties surface, regarding, e.g., the reliability of patient reports, the sensitivity of laboratory tests, and the boundaries of scientific knowledge. The management and portrayal of uncertainty is a critical aspect of professional discourse. This paper documents the rhetorical features of certainty and uncertainty in novice case presentations, considering their pragmatic and problematic implications for students' professional socialization. This study was conducted during the third-year inpatient clerkship at a tertiary care, pediatric hospital in hospital in Canada. Data collection included: (1) non-participant observations of 19 student case presentations involving 11 student and 10 faculty participants, and (2) individual interviews with 11 students and 10 faculty participants. A grounded theory approach informed data collection and analysis. Five thematic categories emerged, two of which this paper considers in detail: "Thinking as a Student" and "Thinking as a Doctor". Within these categories, the management and portrayal of uncertainty was a recurrent issue. Teachers modeled central features of a "professional rhetoric of uncertainty", managing uncertainty of six origins: limits of individual knowledge, limits of evidence, limitless possibility, limits of patient's/parent's account, limits of professional agreement, and limits of scientific knowledge. By contrast, students demonstrated a "novice rhetoric of uncertainty", represented by their focus on responding to personal knowledge deficits through the strategies of acknowledgement, argument, and deflection. Some students moved towards the professional rhetoric of uncertainty, suggesting not only advances in communication, but also shifts in attitude towards patients and colleagues, that were interpreted as indications that this rhetoric shapes professional identity and interactions.