Autoimmune thyroiditis (AIT) is on the rise among the population, and is frequently associated with patients with acne vulgaris, especially females aged between 18–55 years old. The connection between the two is not fully elucidated. In this study, 236 patients diagnosed with acne in the dermatological office of the private Pelican Hospital and in few private dermatological offices from Oradea, Romania, during January 2018–December 2020, aged between 12 and 55 years old, were endocrinologically investigated to determine AIT and its influence on the severity of the acne. The values for the thyroid antibodies and thyroid-stimulating hormone (TSH) were determined for all of the subjects. The frequency of AIT in the study group was 72% and was associated with severe acne (p < 0.001). Patients with AIT with normal or hypofunction had more frequent severe acne than those with hyperfunction (p < 0.001, p = 0.002). The TSH and anti thyroidperoxidase (TPO) values did not influence the severity of the acne (p = 0.494; p = 0.111), while the anti-TG values were associated with severe acne (p = 0.007). The risk analysis indicated that raised values of anti-TPO (2.91 times greater) correlated with high anti-thyroglobulin (TG) values (4.36 times greater) doubled the risk of developing severe acne in patients. In acne evolution, the existence of AIT involves significant modifications.