In a previous paper, the authors found that impairment on the Wisconsin Card Sorting Test (WCST) in adolescence was predictive of bipolar disorder in young adulthood among offspring of mothers with bipolar illness. In the present study, the authors explore the contribution of maternal characteristics, beyond maternal mood disorder, to the prediction of offspring dysfunction on the WCST. Results showed that maternal bipolar disorder and maternal negativity were both predictive of impaired performance on the WCST during adolescence. The contribution of maternal negativity to offspring WCST impairment was not better explained by maternal personality disorder, mother's functional impairment, family loading for bipolar disorder, or offspring disruptive behavioral disturbance. Findings did not support a moderator model. However, support was found for a mediation model in which maternal negativity contributed to risk for offspring bipolar disorder through its negative association with apparent frontal lobe functioning, as measured by the WCST. Findings are discussed from the perspective of a vulnerability-stress model. In addition, the authors consider the possibility that maternal negativity and offspring impairment on the WCST may be reflective of common heritable trait.