Comorbidity among the anxiety disorders is common and may negatively impact treatment outcome. Potentially, transdiagnostic cognitive-behavioral treatments (CBT) deal more effectively with comorbidity than standard CBT. The present study tested the effectiveness of The Unified Protocol (UP) applied to Mental Health Services. Pre-post-treatment effects were examined for psychiatric outpatients with anxiety disorders receiving UP treatment in groups. Forty-seven patients (mean-age = 34.1 (SD = 9.92), 77% females) with a principal diagnosis of anxiety were included. We found significant and clinically meaningful changes in the primary outcomes Clinical Global Impression Severity Scale (CGI-S; d = 1.36), Hamilton Anxiety Scale (HARS; d = .71), and WHO-5 Well-being Index (WHO-5; d = .54). Also, comorbid depressive symptoms and levels of positive and negative affect changed significantly after treatment. Patients with high levels of comorbidity profited as much as patients with less comorbidity; however, these patients had higher scores after treatment due to higher symptom burden at onset. Patients with comorbid depression profited more from treatment than patients without comorbid depression. The treatment effects found in the present study correspond to treatment effects of other TCBT studies, other UP group studies, and effectiveness studies on standard CBT for outpatients. The results indicate that the UP can be successfully applied to a MHS group setting, demonstrating positive effects on anxiety and depressive symptoms for even highly comorbid cases.