A few studies have shown a high prevalence of thyroid autoimmunity in patients with psoriatic arthritis. However, thyroid autoimmunity has not been investigated in patients with psoriasis who do not have psoriatic arthritis. We aimed to investigate thyroid autoimmunity in patients with psoriasis. The study included 105 consecutive patients with psoriasis who did not have psoriatic arthritis and a sex and age matching control group consisting of 96 patients with tinea pedis. All of the patients with psoriasis were examined dermatologically and PASI scores were calculated for each patient. Free triiodothyronine (FT3), free thyroxine (FT4), thyroid stimulating hormone (TSH), antithyroglobulin (AbTG), and antithyroidperoxidase antibody (AbTPO) levels were measured in all of the subjects. The levels of TSH, FT3, FT4, AbTG and AbTPO and ultrasonographic findings of thyroid gland were compared statistically between psoriasis and control groups. Also, the levels of TSH, FT3, FT4, AbTG and AbTPO of psoriasis patients were compared with PASI scores. Mann-Whitney U test was used as statistical method. The mean age of patients with psoriasis was 40.54 +/- 16.91 years. 56 patients were female, 49 were male. The levels FT4 were found to be significantly increased in the patient group. But levels of AbTPO and AbTG were not statistically different between the two groups. The patients who had thyroiditis plus nodules in thyroid ultrasonography had statistically longer disease periods. This is the first study that investigated autoimmune thyroid disorders in patients with psoriasis who did not have arthritis. We believed that thyroid autoimmunity in patients with psoriasis was no different from that found in healthy individuals.