Background/Objectives: Psoriasis is an inflammatory skin disease, which is associated with metabolic syndrome and insulin resistance. Irisin is an adipokine and myokine that regulates the metabolic status during times of increased insulin sensitivity. In this study, we aimed to investigate changes in the serum level of irisin in psoriasis patients in comparison with participants who did not have any disease (control group). We hope the results of our study would also aid in establishing a protocol aimed at understanding the etiopathogenesis and treatment of psoriasis. Materials and methods: The study included 30 patients with psoriasis vulgaris, who presented to the dermatology outpatient clinic and were not receiving systemic treatment. The control group included voluntary participants who did not have any disease (n = 30). In addition to venous and salivary irisin levels, glucose, triglyceride, cholesterol, high-density lipoprotein, and low-density lipoprotein levels, and Homeostasis Model Assessment of Insulin Resistance scores were measured in both control and patient groups. Results: Serum irisin and salivary irisin levels were significantly lower in the patient group compared with the control group (p < 0.05). In the patient group, serum irisin levels had a positive correlation with salivary irisin levels (r = 418; p = 0.022) and a negative correlation with Psoriasis Area and Severity Index (r = -437, p = 0.016) and Dermatological Life Quality Index (r = -424; p = 0.02) scores. Conclusion: This is the first study evaluating irisin levels in patients with psoriasis vulgaris in the literature. The results of our study show that serum and salivary irisin levels were significantly lower in the patient group when compared with the control group. Irisin levels in patients with severe psoriasis were low, suggesting that irisin may have a role in the pathogenesis of psoriasis and may be a marker showing the severity of psoriasis, which could warn us against the development of insulin resistance and diabetes mellitus. Copyright (C) 2016, Taiwanese Dermatological Association. Published by Elsevier Taiwan LLC.