The present study examined whether intolerance of uncertainty (IU) moderates the relationship between catastrophic health appraisals and health anxiety. Specifically, appraisals that ambiguous symptoms are the sign of a catastrophic health concern are proposed to be better tolerated by some individuals (i.e., those with low IU) than others (i.e., those with high IU). A large sample of medically healthy college students (N = 412) completed a scenario-based measure assessing the tendency to attribute ambiguous body sensations and symptoms to either catastrophic (i.e., catastrophic health appraisals) or minor (i.e., minor health appraisals) health concerns, as well as self-report measures of IU and health anxiety. Consistent with predictions, catastrophic health appraisals were only significantly associated with health anxiety at high levels of IU. Moreover, and showing a degree of specificity, IU did not moderate the relationship between minor health appraisals and health anxiety. Conceptual and therapeutic implications are discussed.