This study was designed to provide an estimate of the prevalence of neuropsychological impairment in chronic fatigue syndrome (CFS), to evaluate the concordance between impairment found on standardized tests and self-reported neuropsychological problems, and to study the relationship between neuropsychological functioning and fatigue severity and psychological processes. We adopted an individual approach to determine neuropsychological impairment as contrasted with the group-comparisons approach used in previous studies. Also, correction for premorbid functioning and confounders was done on an individual basis. The results show that a minority of participants were impaired in neuropsychological functioning. There was no relationship between neuropsychological impairment on standardized tests and self-reported memory and concentration problems. Neuropsychological functioning was not related to fatigue or depression. Slowed speed of information processing and motor speed were related to low levels of physical activity.