OBJECTIVES: To determine the proportion of phenylketonuria (PKU) patients managed successfully using current treatment strategies and to highlight a particular group(s) of PKU patients who may be uncontrolled by current treatment. METHODS: This is a non-interventional, retrospective, observational study. To date 4 UK sites have enrolled into the chart review. Information on patients with PKU or tetrahydrobiopterin (BH4) deficiency was collected over a five year period (2004-2008). Data was collated on demographics, diagnosis, number of uncontrolled episodes, interventions made during an uncontrolled episode and the length of time phenylalanine (Phe) levels were above the target level. An uncontrolled episode is defined as three or more consecutive Phe levels above the National Society for Phenylketonuria (NSPKU) guideline. Interventions can include dietary advice, health care professional phone calls, clinic visits, counselling/psychological support, addition or change in use of supplements, social care visits, and hospital admission. Data was analysed to explore the treatment of PKU in practice, the accompanying Phe levels and other health and clinical outcomes. RESULTS: Recruitment is being completed. This information will be reported as a full dataset in the poster. Thus far data has been collected for 102 patients across 3 centres (50% male).  The age range of patients reviewed was 6-60 years. A total of 93% of patients had a diagnosis of PKU, 0% BH4 deficiency and 7% unknown. The average number of uncontrolled episodes per patient per year was 1. An average of 7 interventions were made during each episode. The average length of the episode was 176 days. CONCLUSIONS: There is lack of published data on the management of PKU in clinical practice. This study provides an analysis of current treatment of PKU in clinical practice and its effectiveness on clinical and health outcomes. The majority of PKU patients within this study had well-controlled Phe levels, however a number may benefit from additional treatment.