Background: To examine whether adhering to the Dutch clinical practice guidelines for anxiety disorders is associated with a higher efficiency of care (i.e. cost-effective) compared to guideline-non-adherence. Methods: After the Dutch practice guidelines for anxiety disorders were implemented, adult patients diagnosed with anxiety disorder or hypochondria were approached for participation. Using medical files patients’ treatment was classified as guideline-adherent (N=81) or guideline-non-adherent (N=56). Patients completed questionnaires about severity of symptoms (SCL-90-R) and quality of life (WHOQOL-Bref) before the start of treatment and again one year later. Medical costs and productivity losses were assessed at one-year follow-up. Results: Data of 139 patients for whom the guidelines were applicable were analyzed. From a health care perspective, the guideline-adherent treatment group had lower costs (incremental costs: -€292) and higher effect on the SCL-90-R (incremental effect: 26.17), and therefore dominated guideline-non-adherent treatment on average. There was a 68% likelihood that guideline-adherent treatment was associated with more effects and lower costs. Furthermore, guideline-adherent treatment was associated with an additional 0.09 QALY, indicating that on average more QALYs were generated for fewer costs. Limitations: This study employed an uncontrolled design. Caution should be taken when making causal inferences. Conclusions: Patients who received guideline-adherent treatment are more likely to experience larger symptom reduction and fewer costs during follow-up than patients who do not receive guideline-adherent treatment. The results justify further investigation of the effectiveness of implementing multidisciplinary guidelines.