Abstract: The present invention provides methods for selecting an individual with psoriasis (Ps) or psoriatic arthritis (PsA) who should receive or who is likely to respond to a treatment with an anti-tumor necrosis factor alpha (anti-TNF?) therapy. In addition, provided herein are methods for selecting an individual with Ps or PsA who should receive or who is likely to respond to a therapy that is not an anti-TNF? therapy, e.g., a non-anti-TNF? therapy for the treatment of Ps or PsA. Specifically, the methods of the present invention relate to detecting the presence of distinct alleles of the PDE3A-SLCO1C1 locus which are associated with a clinical response to an anti-TNF? therapy or a non-anti-TNF therapy in patients with Ps or PsA.