<b><i>Background:</i></b> Psoriasis is characterized by multiple genetic variations. Some of these variations, such as the presence of HLA-Cw6 or TNFAIP3 single-nucleotide polymorphisms (SNPs), have been correlated to the response to biologic treatments. <b><i>Objective:</i></b> The aim of our study was to evaluate the effects of IL12B and IL6 SNPs on the response to ustekinumab. <b><i>Methods:</i></b> We retrospectively analyzed the genotypes of 64 patients who had been treated with ustekinumab for up to 1 year. Efficacy data were evaluated using ‘intention to treat-last observation carried forward' analysis. <b><i>Results:</i></b> We confirmed the positive role of HLA-Cw6 as a predictor of the response to ustekinumab and discovered that presence of the GG genotype on the IL12B rs6887695 SNP and absence of the AA genotype on the IL12B rs3212227 SNP significantly increase the probability of therapeutic success in HLA-Cw6 positive patients. <b><i>Conclusions:</i></b> The availability of pharmacogenetic data will influence therapeutic decisions in the clinical management of psoriatic patients.