A 34-year old woman with Generalized Anxiety Disorder and recently diagnosed multiple sclerosis was treated in a single case design. The case formulation approach was used to assess and integrate the various difficulties reported by the participant. Treatment interventions targeted intolerance of uncertainty, overestimation of the utility of worrying, problem orientation, and problem solving. Results indicated a decrease in the tendency to worry. Difficulties in the application of typical interventions for Generalized Anxiety Disorder to people with multiple sclerosis are discussed and suggestions are provided.