Objectives: This study examined rumination as a moderator and mediator between intolerance of uncertainty (IU) and depression and anxiety symptoms. Designs: The study was a cross sectional study. Survey data were collected from 332 undergraduate students at a large Midwestern university. Results: The results from hierarchical analyses supported the moderator role of rumination. A high level of rumination enhanced the association between IU and depression symptoms. In addition, both high and low levels of rumination strengthened the relation between IU and anxiety symptoms. Results from structural equation modeling analyses indicated that rumination fully mediated the relation between IU and depression symptoms, but only partially mediated the association between IU and anxiety symptoms. Conclusions: The results supported rumination as a moderator and mediator in the association between IU and depression and anxiety symptoms. Future research and practical implications are discussed. © 2011 Wiley Periodicals, Inc. J Clin Psychol 67:1–20, 2011.