Children with medium chain acyl coenzyme A dehydrogenase deficiency (MCADD) have been reported to be at high risk for neurocognitive deficits. However this has not been systematically studied and little is known about the exact nature of neuropsychological sequelae or of the impact of early diagnosis and screening on outcome. We examined cognitive and adaptive outcome in children with MCADD (N = 38, age range: 2 years, 2 months - 10 years, 3 months) diagnosed either through a newborn screening program(tandem mass spectrometry/MSMS) or upon clinical presentation. There was no evidence of overall intellectual impairment in either groups but there was some suggestion of poorer verbal and specific executive functioning (i.e., planning) abilities in the unscreened cohorts. Adaptive functioning was relatively intact with the exception of reduced Daily Living Skills in both our screened and unscreened groups. Early diagnosis and greater number of hospitalizations were related to higher verbal, communication, and socialization skills. Overall, our results highlight the importance of early diagnosis and management for children with MCADD.