One of the fundamental concepts in generalized anxiety disorder (GAD) is intolerance of uncertainty (IU), but little was known about the concurrent and temporal patterns of correlations between IU and the intensity of GAD symptoms over the course of therapy. The majority of the currently accessible information also focuses on IU as a unidimensional term, despite the fact that some researchers perceive it as having just 1 dimension—inhibitory IU—and others see it as having 2 dimensions—prospective IU. About 90 GAD patients who were completing group-based cognitive behavior therapy (CBT) for GAD conducted tests of IU and worried intensity at the beginning of treatment, session 4, session 8, and the completion of treatment (session 12). The total IUS score and the inhibitory (but not prospective) subscale score displayed a similar pattern of connections. According to longitudinal multilevel modeling, IU may be able to forecast concern severity in the present but not in the future. Furthermore, over time, there was a growing correlation between IU overall scores and worry levels. Anxiety also grew over time in connection to inhibitory IU (but not prospective IU). When the variables in the model were rearranged, anxiety intensity continued to predict current IU but not future IU. As a result, the direction of the association between IU change and concern change during CBT, particularly as therapy advances, was still uncertain.