Psoriasis is a chronic autoimmune disease affecting the skin and joints, IL- 17 family has been shown to be the major effector cytokine in its pathogenesis. This study aimed to investigate genetic polymorphism of IL-17F (rs763780) and evaluate the impact of this polymorphism on circulating levels of IL-17F as a potential risk locus for psoriasis. 60 patients suffering from chronic plaque psoriasis and 60 healthy controls were genotyped for the IL-17F (rs763780) using an Amplification Refractory Mutation System - PCR (ARMS-PCR) method. Measurement of serum IL-17F was also done by ELISA. There was a significant difference in frequency between TT and TC genotypes (OR= 2.74, 95%CI=1.04 -7.4, P=0.04) and TT and CC genotypes (OR=10.9, 95%CI=1.3-91.3, P=0.007). Moreover, the TC and CC genotypes were associated with increased risk of psoriasis in comparison with the TT genotype. (OR= 3.8, 95% CI: 1.5– 9.4, P= 0.003). The mutant allele, C, was significantly associated with an increased risk of psoriasis compared to that with the wild T allele, T (OR= 4.1, 95% CI: 1.9– 9.1, P= 0.0002). Serum level of IL-17F was higher among psoriasis patients (25.7±3.8pg/ml) than healthy controls ((15.1±2.1pg/ mL). In conclusion, IL17F polymorphism (rs763780) is associated with increased risk of psoriasis and may influence the level of production of IL-17F with subsequent effects on the pathogenesis of psoriasis.