Background: Psoriasis is mediated by a T helper 17 (Th17) cell inflammatory process. This study describes the changes in serum levels of IL-17, 22 and 23 in patients of psoriasis vulgaris treated with narrow band ultraviolet B (NBUVB).Methods: The serum levels of IL-17, 22 and 23 were compared with a control group (n=30) before and after NBUVB. In addition, post-NBUVB levels were compared with healthy controls. Psoriasis Area Severity Score (PASI) and Body Surface Area scoring were used to evaluate severity of disease.Results: When compared with the non-psoriasis control group, IL-17, 22 and 23 were higher in psoriasis patients (p<0.05, p<0.001, p<0.001, respectively). The serum levels of all three interleukins strongly correlated with severity of disease. Although IL-17, 22 and 23 decreased after NBUVB, decline in IL-17 was not significant after phototherapy as compared to controls (p=0.634). IL-22 and 23 continued to remain elevated post-phototherapy when compared with control group (p<0.05, p<0.0001, respectively).Conclusions: The serum levels of IL-17, 22 and 23 decrease after phototherapy in psoriasis. Post-phototherapy only the IL-17 levels decrease to that of non-psoriasis controls. Our study supports the role of T helper 17 cell specific cytokines in psoriasis and a possible mechanism of action of NBUVB via inhibition of these cytokines.