It has recently been reported that persons at risk for Huntington's disease who test positive for the linked restriction fragment length polymorphism on chromosome 4 display neuropsychologic impairments when compared with at-risk subjects who test negative for this marker. We have studied a substantially larger series of at-risk subjects who have been thoroughly screened for the absence of neurologic or psychiatric features of Huntington's disease and have undergone predictive DNA testing. No evidence of cognitive or emotional differences between marker-positive and marker-negative individuals was found. Consideration of the designs and findings of the two studies indicates that it is premature to conclude that there are neuropsychologic impairments in Huntington's disease that precede the clinical onset of the illness.