Ustekinumab (Stelara®) is a human monoclonal antibody that binds to the shared p40 subunit of interleukin (IL)-12 and IL-23, blocking signalling of their cognate receptors. It is established in the treatment of moderate-to-severe plaque psoriasis, but recently received approval in adults with active psoriatic arthritis. Tumour necrosis factor (TNF) inhibitors remain first-line biological agents for the treatment of psoriatic arthritis, but alternative agents are needed. This article summarises the pharmacology of ustekinumab and reviews its use in phase 3 trials in psoriatic arthritis. In these trials, subcutaneous ustekinumab 45 or 90 mg was significantly more effective than placebo, as determined by American College of Rheumatology response criteria at week 24. The drug was also associated with significantly greater efficacy than placebo with regard to secondary endpoints, including the Psoriasis Area and Severity Index ≥75 % response, enthesitis and dactylitis scores, radiographic progression and Health Assessment Questionnaire-Disability Index scores. Response to ustekinumab was maintained during long-term therapy (up to week 100), and was achieved with and without concomitant methotrexate. Ustekinumab was generally well tolerated, and the tolerability profile in psoriatic arthritis was similar to that reported in plaque psoriasis. Throughout long-term ustekinumab treatment, serious infection or major cardiovascular adverse events occurred rarely. More data are needed to clearly define the place of ustekinumab in psoriatic arthritis treatment algorithms. Meanwhile the drug is a valuable additional option for patients with psoriatic arthritis in whom the response to previous non-biological disease-modifying antirheumatic drugs has been inadequate, or for those who have failed anti-TNF therapy.