International PKU Day is observed worldwide every June 28 to educate the public about phenylketonuria (PKU), a rare genetic disorder that affects the metabolism of phenylalanine, an amino acid found in various foods. The day was established in 2013 by the European Society for Phenylketonuria and Allied Disorders Treated as Phenylketonuria (E.S.PKU), which represents numerous patient organizations across Europe. June 28 was chosen to honor the birthdays of Horst Bickel, who developed a low-phenylalanine diet for PKU treatment, and Robert Guthrie, who created a screening method for newborns. Events and activities are organized by E.S.PKU, its member organizations, healthcare providers, and individuals, including patients and their families, to promote understanding of PKU and its management. The observance highlights the importance of early screening and dietary management to prevent severe complications associated with the disorder.