Ustekinumab (Stelara™) is a human monoclonal antibody that binds to the p40 subunit common to both interleukin (IL)-12 and IL-23. It is indicated in the US for use in adult patients with moderate to severe plaque psoriasis who are candidates for phototherapy or systemic therapy. In the EU, it is indicated for those who failed to respond to, have a contraindication to or are intolerant of other systemic therapies or phototherapy. This article reviews the efficacy and tolerability of ustekinumab in patients with moderate to severe plaque psoriasis, as well as summarizing its pharmacological properties. Ustekinumab attenuates the immune cell activation properties of IL-12 and IL-23. It interrupts the abnormal activation of signalling and cytokine cascades that underlie the pathology of psoriasis by reducing the expression of IL-12- and IL-23-induced cell surface markers that mediate skin homing, activation and cytokine release. In well designed, randomized clinical trials, regimens of subcutaneous ustekinumab 45 or 90 mg provided a rapid and durable improvement in psoriasis area severity index (PASI) scores for patients with moderate to severe plaque psoriasis. A significantly greater proportion of patients receiving ustekinuman 45 or 90 mg compared with those receiving placebo achieved a ≥75% improvement from baseline in PASI score following 12 weeks' treatment (primary endpoint). Improvements in PASI scores were evident following 2 weeks' treatment with ustekinumab and were sustained for up to 3 years. Treatment with ustekinumab 45 or 90 mg also improved health-related quality-of-life scores from baseline. Following 12 weeks' treatment, ustekinumab 45 or 90 mg was more effective than etanercept 50 mg twice weekly in providing symptomatic relief for patients with moderate to severe plaque psoriasis. Furthermore, ustekinumab treatment provided effective symptomatic improvement for almost half of the patients who showed no response to 12 weeks' treatment with etanercept. More limited data indicate that ustekinumab also improves the symptoms of arthritis in patients with plaque psoriasis and psoriatic arthritis. Subcutaneous ustekinumab was generally well tolerated in clinical trials; most adverse events were mild in intensity and did not require dosage adjustment. A pooled analysis of clinical trial data indicated no specific patterns of infection for recipients of ustekinumab and that infection rates remained stable following cumulative exposure to the agent. In conclusion, subcutaneous ustekinumab provides an effective and well tolerated alternative for the symptomatic treatment of patients with moderate to severe plaque psoriasis.