Phenylketonuria treatment policies vary not only between different countries worldwide, but also within one country. Recommendations and guidelines for phenylketonuria should deal with the following subjects: 1. What is the target age to start dietary phenylalanine restriction under newborn-screening conditions? 2. At which plasma phenylalanine concentration should phenylalanine restriction be initiated? 3. Which are the recommended plasma phenylalanine concentrations at different ages? 4. What is the recommended frequency of monitoring phenylalanine in plasma? Statements from the following countries are presented: Czech Republic, Denmark, France, Germany, Great Britain, Hungary, Ireland, Poland, Slovakia and the United States.
Conclusion: Due to the lack of internationally accepted guidelines, management of phenylketonuria still varies between different countries. Our efforts should focus on the formulation of internationally acceptable and accepted recommendations for the treatment of patients with phenylketonuria at different ages.