Psoriasis affects 2-3% of the population, causing significant morbidity and financial burden. Immunosuppressive drugs such as cyclosporine are first line systemic therapies for moderate-to-severe forms. However, patients exhibit heterogeneity in their response to therapy, possibly due to genetic factors. The aim of the present study was to assess the ABCB1 T-129C, G1199A, C1236T, G2677T and C3435T single-nucleotide polymorphisms (SNPs) as candidate predictive markers of response to cyclosporine treatment in 84 psoriasis patients. 62% of the patients were defined as responders and 38% as nonresponders. All SNPs complied with Hardy-Weinberg equilibrium. SNP and haplotype analyses were performed to access responsiveness to treatment. Association analysis revealed statistically significant association of SNP 3435 T with negative response (P=0.0075), a result that was further validated in haplotype analysis. This study is the first in the field of the pharmacogenetics of cyclosporine in psoriasis whose results merit further exploitation in larger independent cohorts.