Fears related to anxiety sensitivity (AS)-illness/injury sensitivity, fear of negative evaluation, and fear of pain-may have important theoretical associations with intolerance of uncertainty (IU). In separate investigations, AS and IU have been independently related to the same anxiety-related psychopathology. AS and IU seem to share a basis in fearing unknown, potentially harmful consequences; however, their inter-relationship remains uncertain. IU regarding a specific stimulus, a physical sensation for example, may result in a variety of interpretations and responses, including the catastrophic appraisals that characterize AS. The association between AS and IU was examined in a sample of 293 undergraduates. Results of confirmatory factor and correlation analyses suggest the two constructs are related, but nonetheless independent. It appears that IU may be a required component of catastrophic misappraisals while being an important construct related to fear and anxiety in its own right. Future research directions and potential applications are discussed.