Psoriatic arthritis (PsA) is an inflammatory joint disease that denotes a heterogeneous group of arthritides that may be present with or without obvious psoriatic lesions; therefore, treatment is largely driven by the location and severity of articular and skin involvement. Rheumatologists, who generally manage the disease, commonly divide patients into three segments for the purposes of defining a course of treatment: patients with peripheral arthritis, patients with axial disease, and patients with both peripheral and axial disease. Patients with peripheral disease are generally treated with conventional disease-modifying antirheumatic drugs (DMARDs) first line, after which they may transition to a second conventional DMARD and/or a tumor necrosis factor alpha (TNF-α) inhibitor. NSAIDs are prescribed first line for axial disease, followed by TNF-α inhibitors in the second line of therapy (although payers may require patients fail conventional DMARDs before biologic therapy as in peripheral disease despite the lack of efficacy of conventional DMARDs in treating axial disease). Patients with peripheral and axial manifestations may be treated with NSAIDs and/or conventional DMARDs before anti-TNF-α therapy. Five tumor necrosis factor alpha (TNF-α) inhibitors, including the most recently approved agent in this class—Cimzia (UCB’s certolizumab pegol)—are approved in the United States for PsA, as is the recently approved interleukin (IL)-12/23 inhibitor, Stelara (Janssen’s ustekinumab). Other biological therapies approved to treat rheumatoid arthritis (e.g., Orencia [Bristol-Myers Squibb’s abatacept]) may be prescribed off-label for moderate to severe PsA. Using patient-level claims data, this report tracks the share of disease-modifying PsA drugs through lines of therapy, evaluates treatment flow, and analyzes why certain key therapies are chosen over others.