UNLABELLED: This study aimed to explore the developmental outcomes of children with biotinidase deficiency (BD) and the psychological well-being of their parents. The cohort comprised 61 children diagnosed with BD who were followed at the Department of Pediatric Metabolism of Başakşehir Çam and Sakura City Hospital in Istanbul, along with their parents. The control group comprised 49 children who were admitted to the pediatric outpatient clinic during the same period and did not have any chronic physical diseases or previous psychiatric admissions, and their parents. The current findings indicated that children with BD did not show significant developmental delays compared to the control group, with no notable differences in intelligence scores between the groups. Interestingly, parents of children with BD reported lower levels of state anxiety than those of the control group, although no significant differences were observed for other mental health metrics. CONCLUSION: These findings imply that early diagnosis and intervention through newborn screening could help alleviate developmental and psychological challenges for children and their parents. WHAT IS KNOWN: • Children who receive biotin supplementation before the onset of symptoms generally develop, while those who are untreated may exhibit developmental delays. • Having a child with a metabolic disease can adversely affect a parent's psychological well-being. WHAT IS NEW: • Children diagnosed with BD through newborn screening did not show significant developmental delays compared to the control group, with no notable differences in intelligence scores between the groups. • Parents of children with BD reported lower levels of state anxiety than those of the control group, although no significant differences were observed for other mental health metrics.