Intoxication-type Inherited Metabolic disease (IT-IMD) are a group of rare, chronic diseases. They share the pattern of intoxication by a substance, which accumulates due to a genetically determined enzyme failure. In many IT-IMD, brain toxicity is predominant. Treatment mostly encompasses a lifelong natural protein-restricted diet, supplementation of amino acid solutions and specific medication.(1) The diseases are by definition chronic but according to their characteristics they can be subdivided into having or having not acute, crisis-like episodes. Patients with ITIMD such as urea cycle disorders (UCD) or organic acidurias (OA) may be challenged by life-threatening metabolic crises and acute exacerbations (acute IT-IMD). Many acute IT-IMD patients develop neurocognitive and behavioural problems, often despite sufficient treatment adherence. Furthermore, difficulties to adhere to diet and medication, nausea and vomiting are major every-day complaints.(2) Phenylketonuria (PKU), an inborn error of phenylalanine (Phe) metabolism is a non-acute IT-IMD, patients generally have no metabolic crises or short-term disease exacerbations. Accumulating Phe is toxic to the brain and causes severe, irreversible cognitive impairment. Mainstay of treatment in classical PKU is a lifelong protein-restricted diet complemented with amino acid supplementation.(3)With good metabolic control, classical PKU patients usually achieve normal cognitive functioning, but complaints such as attention problems, anxiety, or depression occur frequently.(2) Acute and non-acute IT-IMD patients face considerable burdens of disease and treatment, which may impair health-related quality of life (HrQoL). HrQoL is 'a patient's perception of the impact of disease and treatment on functioning in a variety of dimensions, including physical, psychological, and social domains.(1,4) Research on the subjective burden of IT-IMD remains sparse. . Previous research suggests that pediatric patients' and their parents' everyday life is significantly affected by the considerable disease and treatment burdens of E-IMD.(5) Studies with appropriate sample sizes are needed to make valid statements about health-related quality of life (HrQoL) in children and adolescents with IT-IMD