ObjectiveThis randomized controlled pilot study investigated the feasibility of a future full-scale RCT to compare the effects of intolerance-of-uncertainty therapy (IUT) and metacognitive therapy (MCT) in primary health care patients with generalized anxiety disorder (GAD). Preliminary treatment effects were also evaluated.Materials and methods64 patients with GAD at a large primary health care center in Stockholm, Sweden, were randomized to IUT or MCT. Feasibility outcomes included participant recruitment and retention, willingness to receive psychological treatment, and therapists’ competence in and adherence to treatment protocols. Self-reported scales were used to assess treatment outcomes, including worry, depression, functional impairment, and quality of life.ResultsRecruitment was satisfactory, and dropout was low. On a scale from 0 to 6, participants were satisfied with participating in the study (M = 5.17, SD = 1.09). Following brief training, therapists’ competence was rated as moderate, and adherence was rated as weak to moderate. From pre- to post-treatment, reductions on the primary treatment outcome measure of worry were of a large effect size and statistically significant in both the IUT and MCT conditions (Cohen’sdfor IUT = -2.69, 95% confidence interval [-3.63, -1.76] anddfor MCT = -3.78 [-4.68, -2.90]). The between-group effect size from pre- to post-treatment was large and statistically significant (d= -2.03 [-3.31, -0.75]), in favor of the MCT condition.ConclusionIt is feasible to carry out a full-scale RCT to compare the effects of IUT to MCT for patients with GAD in primary health care. Both protocols seem effective, and MCT seems superior to IUT, but a full-scale RCT is needed to confirm these conclusions.Trial registrationClinicalTrials.gov (no.NCT03621371).