A formal modeling approach was used to characterize decision-making processes in bipolar disorder. Decision making was examined in 28 bipolar patients (14 acute and 14 remitted) and 25 controls using the Iowa Gambling Task (Bechara et al., 1994), a decision-making task used for assessing cognitive impulsivity. To disentangle motivational and cognitive aspects of decision-making processes, we applied a formal cognitive model to the performance on the Iowa Gambling Task. The model has three parameters: The relative impact of rewards and punishments on evaluations, the impact of recent and past payoffs, and the degree of choice consistency. The results indicated that acute bipolar patients were characterized by low choice consistency, or a tendency to make erratic choices. Low choice consistency improved the prediction of acute bipolar disorder beyond that provided by cognitive functioning and self-report measures of personality and temperament.