© 2022 Wiley Periodicals LLC.Background: There may be an association between increased intestinal permeability and the progression of alopecia areata (AA). Objective: The present study aimed to investigate the role of intestinal permeability in the etiopathogenesis of AA and its association with the severity of the disease. Methods: Serum zonulin levels of 70 patients with AA who were not receiving any systemic treatment and of 70 healthy control subjects were measured. Results: The median serum zonulin level in the patient group (46.38 ng/mL) did not differ significantly from that in the control group (50.34 ng/mL) (p = 0.828). Moreover, there was no significant relationship between serum zonulin levels and the severity of the disease (p = 0.549). Limitations: The present study had a cross-sectional design, and it did not include patients with alopecia totalis (AT) or alopecia universalis (AU). Conclusion: We did not observe an increase in intestinal permeability secondary to zonulin expression in patients with AA. However, in order to generalize this result to all patients with AA, serum zonulin levels need to be evaluated in studies including more patients with severe disease, AT, and AU.