Learning and dialogue may naturally engender feelings and expressions of uncertainty for a variety of reasons and purposes. Yet, little research has examined how patterns of linguistic uncertainty are enacted and changed over time as students reciprocally influence one another and the dialogical system they are creating. This study describes the occurrence of uncertainty expressions of graduate students collaborating in computer-mediated discussions to negotiate and construct understandings of new concepts from course readings. We report on how often uncertainty was expressed in online synchronous and asynchronous discussions and the characteristics of its expression. We also explore the antecedents and consequences of such expression. Findings indicate that students expressed uncertainty often and in many ways and that such expression seemed to be integrated in a dynamic system of influences on the conversation. We conclude that the ability to deal with and express uncertainty appropriately is an important skill in online academic contexts that may be related to the intellectual work of students in the process of appropriating the discourse of their academic disciplines as they make meaning of scholarly texts. (Contains 2 tables and 2 figures.)