The authors aimed to investigate cognitive performance of first-degree relatives of probands with bipolar disorder (BD). They hypothesized that the relatives of BD patients would have impaired performance on cognitive tests of frontal-executive functions. A neuropsychological battery was administered to 34 first-degree relatives of BD probands and 25 control subjects. Relatives showed significant impairment in verbal working memory and executive function. Verbal memory and psychomotor performances of relatives were not different from control subjects. One particular component of executive function, cognitive flexibility, was associated with family history of mood episodes with psychotic features. Verbal working memory and executive function deficits may be useful endophenotypic markers of genetic vulnerability to BD.