Long-term follow-up of neuropsychological functioning in metabolic disorders remains difficult due to limited opportunities for comprehensive neuropsychological evaluations. This study examined the validity of using the Adaptive Behavior Assessment System, Second Edition (ABAS-II), and the Behavior Rating Inventory of Executive Function (BRIEF) for assessing developmental status in metabolic disorders and for identifying individuals at risk for cognitive deficits. Results from individuals with urea cycle disorders, phenylketonuria, galactosemia, and fatty acid oxidation disorders were obtained on the ABAS-II and BRIEF and were compared to results obtained from neuropsychological testing performed on the same day. Correlations between scores on the ABAS-II and developmental or IQ tests for individuals with urea cycle disorders ranged from 0.48 to 0.72 and concordance rates for scores greater than a standard deviation below the normative mean ranged from 69 to 89%. Correlations ranged from 0.20 to 0.68 with concordance ranging from 73 to 90% in the other metabolic disorders. For the BRIEF, correlations with other tests of executive functioning were significant for urea cycle disorders, with concordance ranging from 52 to 80%. For the other metabolic disorders, correlations ranged from -0.09 to -0.55. Concordance rates for at-risk status on the BRIEF and executive functioning tests ranged from 55% in adults to 80% in children with other metabolic disorders. These results indicate that the ABAS-II and BRIEF together can confidently be used as an adjunct or supplementary method for clinical follow-up and for research on functional status involving infants, children, and adults with metabolic disorders.