Objectives: The aim of the present study was to compare intolerance of uncertainty and worry among patients with generalized anxiety disorder (GAD), obsessive-compulsive disorder (OCD) and normal individuals. Method: Thirty one patients with GAD, thirty one patients with OCD and thirty one normal individuals were selected via inconvenient sampling. Data gathering was done using Intolerance of Uncertainty Scale (IUS) and Penn State Worry Questionnaire (PSWQ). The data were analyzed in multivariate analysis of variance model (MANOVA). Results: The results showed significant differences in the subscales “uncertainty leads to the inability to act” and “uncertainty is stressful and upsetting”, and in “worry” between three groups of GAD, OCD and normal (p<0.0001). The differences between OCD and GAD groups with normal group were significant in intolerance of uncertainty and two subscales: “unexpected events are negative and person should avoid them” and “uncertainty is unfair” (p<0.0001). Conclusion: Intolerance of uncertainty is a common feature of OCD and GAD. Coping strategies for decreasing uncertainty differentiate these two disorders.