This is a 10-year multi-center, global, observational study to further characterize the safety profile of pegvaliase, including hypersensitivity reactions, long-term safety and tolerability, and the effectiveness of the additional risk minimization measures (aRMMs) (European Union (EU) only) in subjects receiving pegvaliase for the treatment of PKU. Subjects for whom a clinical decision has been made that they will receive pegvaliase to treat their PKU within 30 days following the date of enrollment (incident-users) or have previously started treatment with pegvaliase at the date of enrollment (prevalent-users) are eligible for participation in this study.

This is a 10-year multi-center, global, observational study to further characterize the safety profile of pegvaliase, including hypersensitivity reactions, long-term safety and tolerability, and the effectiveness of the aRMMs (EU only) in subjects receiving pegvaliase for the treatment of PKU. Subjects for whom a clinical decision has been made that they will receive pegvaliase to treat their PKU within 30 days following the date of enrollment (incident-users) or have previously started treatment with pegvaliase at the date of enrollment (prevalent-users) are eligible for participation in this study. Once the subject has been enrolled, the investigator (ie, subject's primary physician) will be asked to provide information about the subject's medical history, treatment(s) received to manage their blood Phe levels, treatment with pegvaliase, and concomitant medication use. The investigator will also be asked to provide evaluation of the following safety concerns: Acute systemic hypersensitivity reaction, Anaphylaxis, Angioedema, Serum sickness, Severe hypersensitivity reaction, Severe or Persistent arthralgia, Severe injection site reaction, Hypophenylalaninemia and other protocol-defined safety events, following the initiation of pegvaliase therapy. There are no protocol-mandated visits or procedures associated with this study. Enrolled subjects should be followed per routine clinical practice at the institution based upon their diagnosis, with clinical outcomes assessed at regular intervals (typically every month during the induction and titration phases of pegvaliase treatment and every 6 months once the maintenance phase is reached). No experimental treatment or assessments are planned as part of this observational study. An Independent Adjudication Committee (IAC) will periodically review protocol-defined safety events, including Acute systemic hypersensitivity reaction and Serum sickness.

Inclusion Criteria:

• Documented diagnosis of PKU per local standard of care
• Currently receiving or planned to receive pegvaliase treatment within 30 days after the date of enrollment, including subjects who previously received pegvaliase as part of the clinical development program and have completed study participation.
• Subject (or legally authorized representative) is willing and able to provide written informed consent after the nature of the study has been explained and prior to any data collection.

Exclusion Criteria:

• Subject has any kind of disorder that, in the opinion of the investigator, may compromise the ability of the subject to give written informed consent and/or comply with any aspect of the study.
• Currently participating in an interventional study of any investigational product, device, or procedure
• Previously enrolled in this study (eg, subjects who have been withdrawn from the study and wish to participate again at a later date)
• German subjects <16 years if age

All subjects with PKU followed at participating centers, currently receiving or planning to receive pegvaliase treatment.