Cognitive impairment remains understudied in generalized anxiety disorder (GAD), despite the high prevalence and substantial burden associated with this disorder. We aimed to assess cognitive impairment in patients with GAD and evaluate the ability of cognitive tests to detect this disorder. Because of its high rate of comorbidity, we also examined how other anxiety disorders and current major depressive episodes affected our results. We tested 263 consecutive general practice outpatients. We used the GAD-7 and the Mini International Neuropsychiatric Interview (MINI) to detect anxiety and mood disorders. We assessed cognitive performance with the Stroop test, a facial emotion recognition test, and the trail-making test (TMT). Compared to patients without GAD, patients with GAD were significantly slower to complete the TMT(B-A) and faster to recognize emotions, especially negative ones such as disgust and anger. When controlling for other anxiety disorders and current major depressive episode, GAD retained a significant effect on the TMT(B-A), but not on the emotion recognition test. The TMT(B-A) could detect GAD with good accuracy (area under the curve (AUC) = 0.83, maximal Youden's index = 0.56), which was by no means comparable to the GAD-7 (AUC = 0.97, Youden's index = 0.81). While it is not efficient enough to replace the GAD-7 as a diagnostic tool, the capacity of the TMT(B-A) to detect GAD emphasizes the importance of cognitive flexibility impairment in GAD.