Background: Alopecia areata) AA (is a non-scarring skin disease affecting the scalp or other body parts. The etiology of AA is still controversial and various pathogenic causes are under investigations. It is characterized by infiltration of T helper 17 cells the hair follicles and chemokine secretion. Objectives: The aim of the current work was to measure serum level of IL-17A in patients with AA and healthy controls to demonstrate if it has a role in the pathogenesis of A.A. and to correlate disease severity with its level. Patients and methods: This case control study included a total of 26 A.A. patients, and 26 age and gender matched healthy controls, attending at Department of Dermatology, Venereology and Andrology, Faculty of Medicine, Ain-Shams University Hospitals, and Department of Dermatology, Venereology and Andrology, National Research Centre, Egypt. Serum level of interleukin-17 was measured. Clinical type, and the severity of the disease were determined for each A.A. patient. Results: Serum level of interleukin-17 was significantly higher in A.A. cases compared to unaffected controls. The interleukin-17 level among A.A. patient was ranged from 133 to 326 (med. 195) pg /ml, while among controls, the level was ranged from 14 to 226 (med. 48) pg /ml. Also, no statistically significant differences were found between interleukin-17 levels regarding the clinical types, age, gender, disease duration, and severity. Conclusion: The significantly high concentration of serum interleukin 17 in A.A. patients supports the theory of its contribution in the process of the hair follicular destruction. It could also be concluded how beneficial its inhibitors can be especially in resistant cases of A.A.