The purpose of this study is to monitor the long-term safety of ustekinumab in pediatric participants (6 years to 17 years of age at the time of inclusion) with moderate to severe plaque psoriasis, through monitoring for the following adverse events potentially related to immune modulation: serious infections, malignancies and autoimmunity; and to monitor the long-term effects of ustekinumab on growth (weight, height, body mass index) and development (sexual maturity based on the Tanner Scale).