Glutaric aciduria type I (GA-I) is an inherited metabolic disorder that may lead to severe motor disorder and cognitive impairment. GA-I is now included in the newborn screening programme in many countries as early detection allows for prompt treatment and effectively reduces the risk of poor developmental outcome. Information regarding the long-term neurodevelopmental outcome of children with GA-I treated early is sparse.We recruited children with a confirmed diagnosis of GA-I diagnosed via newborn screening, treated in our centre and >3 years of age (n = 6). Children were assessed at two time points using a comprehensive neuropsychological test battery. Four of these had been the subject of a previous report. All participants were male, 3-6 years at the initial assessment and 6-12 years of age at the follow-up assessment.Fine motor skills were below average in all patients. Speech, which was affected in all four patients reported previously, improved following speech therapy. IQ scores remained generally stable within the normal range. Executive functioning was average to high average in four patients. Behaviour, as assessed through parental questionnaires, was problematic in two patients. Compounding factors included child neglect, family history of autism and multiple admissions to hospital (n = 1 in each).GA-I affects fine motor skills and speech, regardless of early treatment, but not IQ scores. Patients with GA-I should be referred for assessment and appropriate early intervention. Further research is needed to correlate specific neuropsychological deficits with neuroimaging.