Summary:Deep white matter hyperintensity signals (HI) on magnetic resonance scanning have been reported in normal individuals, especially with age, and have been thought to be clinically insignificant. In contrast, we have found that healthy, young (mean age = 35.2 years) men with HI appear to have a significantly lower attention capacity than a sex- and age-matched control group without HI; healthy, young women with and without HI failed to differ from one another in neuropsychological performance. The findings suggest that hyperintensity signals in men may be associated with subtle neurobehavioral impairment that is only revealed under high demand conditions.