BACKGROUND: The efficacy and safety profile of ustekinumab with up to three years of exposure suggested a favorable benefit-risk profile in patients with moderate to severe psoriasis. OBJECTIVE: To evaluate the safety of ustekinumab in patients with moderate to severe psoriasis treated for up to four years. METHODS: Safety data were pooled across four Phase II/III randomized controlled trials. Rates over time and cumulative rates of adverse events (AEs), AEs leading to treatment discontinuation, serious adverse events (SAEs), serious infections, malignancies, and major adverse cardiovascular events (MACE) (i.e., cardiovascular death, myocardial infarction [MI], or stroke as adjudicated by an independent panel of academic cardiologists) were evaluated. Observed rates of AEs of interest were compared with those expected in the general (malignancies, MI, and stroke) and psoriasis (serious infections, MI, and stroke) populations. RESULTS: Overall, 3,117 patients were followed for up to four years (6,791 patient-years). Rates of AEs, AEs leading to treatment discontinuation, and SAEs remained stable over time, whereas cumulative rates were generally comparable between patients who received 45 mg and 90 mg of ustekinumab. The rates of AEs of interest also remained stable over time, and cumulative rates per 100 patient-years were 0.80 and 1.32 (serious infections), 0.70 and 0.53 (nonmelanoma skin cancer), 0.63 and 0.61 (other malignancies), and 0.56 and 0.46 (MACE) in patients treated with 45 mg and 90 mg, respectively. Rates of AEs of interest were consistent with those in the general and psoriasis populations. CONCLUSION: The safety profile of long-term ustekinumab treatment with up to four years of continuous use remains consistent with previous reports, with no evidence of cumulative toxicity.