The present studies demonstrate that daily worry level is predictive of cognitive processing differences and that these differences are an effect of negative thoughts. In Study 1, worriers (those who reported 50% or greater daily worry) and non-worriers performed a categorization task. The groups did not differ when the stimulus was a clear member or non-member of the category. Worriers showed a significant disruption in processing as the ambiguity of the category membership increased. Study 2 demonstrated that the disruption arose as a result of increased levels of negative thoughts. Worriers and non-worriers were assigned to two conditions, either O-worry ("Relax and let your mind wander for 15 minutes") or 15-worry ("Worry as you typically would for 15 minutes"). Non-worriers evidenced the same disruptive effects in the 15-worry condition as worriers in that condition and worriers in Study 1. Similarly, worriers in the O-worry condition showed a reduction in disruptive effects. The findings are taken as indicating that worry is accompanied by changes in cognitive processing and that these changes are similar for worriers and non-worriers.