Intra-individual variability (IIV) is defined as systematic within-person variation in performance either across test sessions (e.g., test/retest performance on the same task) or in one session (e.g., variations in performance on multiple trials of a single task). Higher levels of IIV have been noted as a characteristic of neurodevelopmental disorders such as attention deficit/hyperactivity disorder (ADHD), but IIV is yet to be investigated in fetal alcohol spectrum disorder (FASD). FASD is a term used to describe a range of conditions resulting from prenatal exposure to alcohol. As part of a comprehensive neuropsychological battery, four study groups (1. fetal alcohol syndrome/partial fetal alcohol syndrome; 2. static encephalopathy/alcohol exposed; 3. neurobehavioral disorder/alcohol exposed as diagnosed using the University of Washington FASD 4-Digit Code; 4. typically-developing (TD) age-matched children with no prenatal alcohol exposure) were administered measures of motor response and inhibitory control, attention, and adaptive behavior. The results indicate increased levels of IIV in those with FASD compared to the TD controls. It was found that IIV uniquely contributes to predicting adaptive behavior above and beyond attention, while attention partially mediates the relationship between IIV and adaptive behavior. This is the first study to the authors' knowledge to show the presence of increased IIV in children with FASD. It additionally provides evidence that IIV measures some inherent variability in performance independent of poor attention in children with FASD.