Psoriatic arthritis (PsA) is an inflammatory arthritis associated with psoriasis. The etiology of PsA is unknown; however, there is mounting evidence for a strong genetic contribution to PsA. A few disease-related genes have already been identified in PsA. Cytokines associated with PsA appear to be the most promising targets for pharmacogenetics. Blockade of TNF-alpha and IL-12/23 is associated with a marked clinical response to PsA and/or psoriasis, implying a pivotal role of these cytokines in the pathogenesis of these two disease entities. To date, only the -308 variant of the TNF-alpha promoter gene has been shown to be important in predicting response to TNF-alpha blockade in inflammatory arthritis.