Phenylketonuria (PKU) is a rare inborn error of metabolism that affects the ability of patients to metabolise phenylalanine (Phe). Lifelong management of blood Phe levels is required in order to avoid the complications associated with PKU. This constitutes a severely protein restricted diet, and regular monitoring of Phe levels. Management of PKU may be costly and time-consuming for adult patients or caregivers of PKU-affected children. A cross-sectional study was performed with patients or their caregivers in the Netherlands to gain insight into the personal time burden and cost of living with PKU. A systematic literature review was performed to identify all aspects of PKU management that may pose a financial or time burden on patients or caregivers. Findings were confirmed through interviews with PKU experts and feedback from patients and caregivers, and consolidated into a questionnaire that aimed to evaluate the impact of each of these factors. Early and continuously treated adult patients and caregivers from seven metabolic centres were recruited to complete the questionnaire online. 22 adult patients and 24 caregivers participated in the study. Managing a Phe-restricted diet represented an extra time burden of 1h and 24min for caregivers and 30min for adult patients per day. Caregivers reported a significantly higher time burden than adult patients. The median total out-of-pocket cost (OOPC) for patients was €604 annually, with 99% of expenditure on low-protein food products. Greater disease severity was significantly associated with increased OOPC and time burden for both adult patients and caregivers. Management of PKU is associated with a considerable time burden for both caregivers of children with PKU and adult patients. Caregivers of PKU-affected children reported a significantly higher time burden than adult patients. The OOPC of caregivers and patients was mainly driven by the expenditure on low protein food. •First study to investigate the time burden and cost of living with PKU.•46 PKU patients completed a web based questionnaire.•Management of PKU poses a considerable time burden on PKU patients.•Greater disease severity was associated with increased time burden and costs.