Background:Psoriasis is a chronic inflammatory skin disease that is now considered a prototypic Th17-mediated disease. The possible role played by vitamin D deficiency in its pathogenesis has been previously highlighted. A number of reports have verified the existence of an interplay between them, however whether such a relation exists between both culprits in the context of psoriasis has not been verified yet.Aim of work:Investigate whether a relation exists between both the interleukin-17 and the vitamin D levels in the psoriatic environment.Patients and methods:Forty-eight histopathologically proven psoriatic patients and 40 age, sex, skin phototype, socioeconomic matched controls were included. Full clinical examination was done and serum levels of IL-17 and 25 hydroxy vitamin D were measured by ELISA.Results:In patients serum IL-17 levels were significantly higher (10.54 ± 0.38pg/ml), whereas serum 25 hydroxy vitamin D levels were significantly lower (21.05 ± 3.66ng/ml) in comparison to controls (p= 0.000) with cutoff values of 6.44 pg/ml, 29.45ng/ml respectively determined by ROC analysis. No significant correlations were detected between serum levels of both IL-17 and 25 hydroxy vitamin D and neither of them showed any significant association with any of the demographic or clinical variables.Conclusion:Our study highlights the possible role played by IL-17 and vitamin D insufficiency in the complex pathogenesis of psoriasis, with a possible but unproven intertwined relation between both opponents. Still larger scale studies are needed to identify mechanisms behind vitamin D insufficiency and the exact immune-regulatory role it plays in psoriasis.