A Study of Ustekinumab in Pediatric Participants (U-POPS) With Juvenile Psoriatic Arthritis or Psoriasis

Inclusion Criteria: * Greater than or equal to (\>=) 5 to less than (\<) 18 years of age, inclusive, with a diagnosis of juvenile psoriatic arthritis (jPsA) (that is, International League Against Rheumatism \[ILAR\] or Vancouver criteria) by qualified health care professional (HCP) * \>=6 to \<18 years of age, inclusive, with a diagnosis of pediatric psoriasis (PsO) by a qualified HCP * Initiated ustekinumab treatment \>=16 weeks prior to enrollment and received 3 or more doses of ustekinumab prior to enrollment * Parent(s) (preferably both if available or as per local requirements) (or their legally acceptable representative) must sign an informed consent form (ICF) indicating that he or she understands the purpose of, and procedures required for, the study and is willing to allow the child to participate in the study. Assent is also required of children capable of understanding the nature of the study (typically 7 years of age and older) as described in informed consent process Exclusion Criteria: * Has poor tolerability of venipuncture or lack of adequate venous access for required blood sampling * Has any condition that, in the opinion of the investigator, participation would not be in the best interest of the participant (example, compromise the well-being) or that could prevent, limit, or confound the protocol-specified assessments * If currently enrolled in an investigational study, contact the study responsible physician to discuss eligibility for inclusion in stud…