Classic systemic treatments for psoriasis have not fully met the needs of patients for permanent improvement. Antibody-based or fusion proteinbased selective targeting of key mediators of inflammation has been added to the treatment approaches for psoriasis. Kong Our study demonstrated that IL-18 expression in the psoriatic lesions before treatment was significantly correlated with the severity of psoriasis and disease duration. No correlation was noted between IL-18 expression and patients' age, smoking status, predisposing factors or coexisting diseases. Flisiak et al. [9] found a significant correlation between plasma IL-18 levels and PASI values. But they did not find any correlation between IL-18 concentration in scales and PASI score. Trinquet et al. [28] studied the influence of disease duration on gene expression profiles in psoriasis. They did not reveal any correlation. However, Craven et al. [29] studied IL-10 in early and late onset psoriasis and confirmed that IL-10 expression was correlated significantly with disease duration. Sampogna et al. [30] studied 380 patients with psoriasis and did not find any significant difference between older and younger patients regarding IL-18 levels. On the other hand, Chen et al. [31] found a statistically significant correlation between IL-18 expression levels and age, with a P value of 0.015.