The present article describes two experimental studies investigating whether individual differences in intolerance of uncertainty (IU) predict worry in response to uncertain situations. In both studies, undergraduate students completed the Intolerance of Uncertainty Scale (IUS; Freeston, Rheaume, Letarte, Dugas, & Ladouceur, 1994) and then completed an intelligence task, which was thought to elicit feelings of uncertainty. After completing the task, state worry was measured. Results of both studies showed that there were positive correlations between IUS scores and task-related state worry. Furthermore, Study 2 showed that individual differences in IU only were predictive of worry in a situation that elicits low to medium levels of uncertainty, and not in a situation high in uncertainty. Thus, only under certain conditions IU-related personality characteristics seem to be predictive of worrisome thoughts.