+Cognitive behavioural therapy (CBT) is an effective treatment for anxiety disorders. However, fewer than 50% of people with anxiety disorders undergo appropriate treatments, with reasons including lack of therapists and high therapy costs. A proposed alternative to mitigate costs and improve accessibility is Internet-delivered CBT (iCBT), which consists of online modules with and without an online therapist assisting. However, there is reluctance for therapists to use iCBT due to low adherence, concerns about addressing complex symptoms, and not being able to form strong interpersonal relationships. Therefore, a blended CBT (bCBT) approach has been proposed, combining iCBT with face-to-face CBT (ftfCBT): A feasibility randomized controlled trial was done with 18 participants randomized to either treatment, finding no difference between these groups in reduction of anxiety symptoms. The current randomized controlled trial aimed to investigate the acceptability, cost-effectiveness, and clinical effectiveness of bCBT compared to ftfCBT, for patients with panic disorder (PD), social anxiety disorder (SAD), and generalized anxiety disorder (GAD) in outpatient care. In total, there were 52 patients randomized to bCBT and 62 to ftfCBT, with a mean (SD) age of 36.3 (10.6). The bCBT group received 15 weekly sessions alternating between face-to-face and online modules with asynchronous feedback from the therapist. Questionnaires at baseline, week 7 (mid-treatment), week 15 (post-treatment), and 1 year follow-up were used to assess the outcomes of acceptability (such as treatment adherence, treatment preference, and satisfaction) and clinical effectiveness (using the Beck Anxiety Inventory (BAI)). The results showed that adherence was not significantly different between the groups, with bCBT being slightly higher (67.4% versus 61.6% completing all sessions, p = 0.608). There was also no difference in ratings of the therapeutic alliance, using the Working Alliance Inventory (WAI-SR), from both the patients’ (p = 0.912) and therapists’ perspectives (p = 0.762). Treatment satisfaction was also not different (p = 0.750), with the mean Client Satisfaction Questionnaire (CSQ-8) scores for both falling between “somewhat satisfied” and “very satisfied”. Furthermore, there were no significant differences in BAI score, representing decreased anxiety severity, between the two groups post-treatment and at 1-year follow-up (p = 0.477 and 0.093 respectively). In terms of cost-effectiveness, bCBT was significantly cheaper for direct medical costs, which were €3758 for bCBT and €3841 for ftfCBT during the 1-year period (mean difference -83.78, 95% CI -96.96 to -70.61, p < 0.001). For societal costs, which included medical, patient, and productivity costs, were not different between the two treatments (€10,945 for bCBT, €10,937 for ftfCBT, mean difference 26.46, 95% CI -24.64 to 42.71, p > 0.01). Overall, this study demonstrated that bCBT is as clinically effective as ftfCBT for anxiety disorders, and is equally acceptable to patients and therapists while being more cost-effective in terms of direct medical costs. However, further randomized trials with greater sample sizes will be needed to strengthen and validate these findings.