Inclusion Criteria:- Patients with PKU from age 10 years requiring dietary and / or pharmacological treatment according to locally applied guidelines  Parents of patients with PKU aged 10 to 18 years requiring dietary and / or pharmacological treatment according to locally applied guidelines Ability and willingness to answer the questionnaires and follow the study procedures Informed consent as documented by signature  Exclusion criteria for patients and parents :  Inability to follow the procedures of the study, e.g. due to language problems or severely reduced health status Pregnant patients or patients who have disclosed to their physician that they are planning a pregnancy in the near future Hyperphenylalaninaemia or mild forms of PKU or other inborn errors associated with elevated Phe but not requiring dietary and / or pharmacological treatment according to locally applied guidelines No inform