Background; Mucopolysaccharidosis (MPS) is a rare, inherited, metabolicstorage disorder. There are seven known subtypes, with each one displayinggenotypic and phenotypic heterogeneity, producing a spectrum of clinicaldisease, and ranging from attenuated to severe. Historically children had ashort life span with death in adolescence. Disease modifying treatmentssuch as hematopoietic stem cell transplants for MPS I-H and enzymereplacement therapy for attenuated MPS I and MPS II, have transformedthis into a chronic illness with survival into early adulthood. However,these children continue to carry a marked burden of disease, with significantmorbidity. The impact of disease on the quality of life of the affectedchildren remains poorly understood, with no previous work looking atpatients' perception of their own health, an important domain whenconsidering the impact of treatment. These children also suffer with headand neck problems, including obstructive sleep apnoea and deafness.Aim; Through this study, we aimed to explore the impact of the disease onthe lives of the children, using the principles of grounded theory research.Method; Children and their parents were invited to participate in semistructuredinterviews. The transcribed interviews were coded and emergentthemes explored until saturation occurred.Results; The families of eleven children with MPS I and seven with MPS IIwere interviewed. Data analysis showed that in MPS I, the presence ofairway disease had a profound impact on the emotional well being ofparents whilst musculoskeletal disease had the biggest impact on the qualityof life of the children themselves, causing chronic pain, restricted mobility,loss of independence and a loss in confidence. In MPS II, parents worriedabout their child's ability to fit-in with their peers and achieve social andfinancial independence. The biggest challenge described by the childrenwith MPS II themselves was from their deafness and language delay.Conclusion; This is the first study to identify aspects of living with MPSthat patient's and their parents find most challenging. The themes toemerge from this work may form the domains of a new disease specificqualitative outcome measure. This exploratory work will also serve toimprove the understanding that health care professionals have of the impactof disease on the lives of these children and their families.