BACKGROUND: Ustekinumab targets interleukin (IL)-12 and IL-23 in the treatment of moderate-to-severe psoriasis. OBJECTIVE: To evaluate overall pooled study data to assess the safety profile of ustekinumab through 3 years of treatment. METHODS: Cumulative safety data were pooled from studies in 3117 ustekinumab-treated patients. RESULTS: During the placebo-controlled periods (Phase 2, PHOENIX 1, PHOENIX 2), rates of adverse events (AEs) were comparable among patients treated with placebo (50.4%), with ustekinumab 45 mg (57.6%), or with ustekinumab 90 mg (51.6%); similar findings were observed during the controlled period of the ACCEPT trial (etanercept: 70.0%; ustekinumab 45 mg: 66.0%; and ustekinumab 90 mg: 69.2%). Rates of serious AEs (SAEs) through the controlled periods were low and comparable among all groups (1.2% to 1.9%). Through 3 years, rates of AEs per 100 patient-years of follow-up (/100 patient-yrs) (45 mg: 305.2/100 patient-yrs; 90 mg: 305.9/100 patient-yrs) and SAEs (45 mg: 6.8/100 patient-yrs; 90 mg: 8.2/100 patient-yrs) were comparable between ustekinumab doses. No cases of demyelination or tuberculosis were reported in these trials. No dose response in rates of AEs, overall infections, or SAEs was apparent through 3 years. Rates of AEs, infections, SAEs, and AEs leading to study agent discontinuation remained generally stable or decreased over time. LIMITATIONS: Controlled periods did not extend beyond 12 to 20 weeks. Only 1247 of the 3117 ustekinumab-treated patients were treated for 2 or more years. CONCLUSIONS: The safety profile of continued ustekinumab exposure through up to 3 years is favorable and consistent with previous short-term reports.