PURPOSE: Inborn errors of metabolism (IEM) are known with poor long-term health concerns; however, the health-related quality of life (HRQoL) and the burden placed on families remain unclear. This study investigated the self- and proxy-reported HRQoL of pediatric patients with IEM with or without developmental disabilities and the burden placed on their caregivers. METHODS: Patients with IEM aged 8-15 years and their caregivers were asked to respond to the Pediatric Quality of Life Inventory (PedsQL), EuroQoL five-dimension questionnaire for younger populations (EQ-5D-Y), and Japanese version of the Zarit Caregiver Burden Interview (J-ZBI). We compared EQ-5D-Y scores with matched EQ-5D-Y population norms. Intraclass correlation coefficients (ICC) for self and proxy HRQoL scores of those without developmental disabilities were calculated. Correlation coefficients of HRQoL proxy responses with J-ZBI score were estimated. RESULTS: We included 66 patients with IEM (mean age, 11.5 years; males, 41.2%) in the study. The mean (± standard deviation) EQ-5D-Y scores without and with developmental disabilities were 0.957 (± 0.071) and 0.821 (± 0.175), respectively. The EQ-5D-Y scores significantly increased compared with the reference values (p < 0.01, effect size = 0.337). The ICC values were 0.331 and 0.477 for the EQ-5D-Y and PedsQL scores, respectively. HRQoL proxy scores had strong negative correlations with J-ZBI scores. CONCLUSION: The HRQoL of patients with IEM without developmental disabilities in our study was similar to that of the general Japanese population. The HRQoL of patients with IEM with developmental disabilities was low and associated with a tendency towards an increased burden of care.