Human decision-making involving independent events is often biased and affected by prior outcomes. Using a controlled task that allows us to manipulate prior outcomes, the present study examined the effect of prior outcomes on subsequent decisions in a group of young adults. We found that participants were more risk-seeking after losing a gamble (riskloss) than after winning a gamble (riskwin), a pattern resembling the gambler's fallacy. Functional MRI data revealed that decisions after riskloss were associated with increased activation in the frontoparietal network, but decreased activation in the caudate and ventral striatum. The increased risk-seeking behavior after a loss showed a trend of positive correlation with activation in the frontoparietal network and the left lateral orbitofrontal cortex but a trend of negative correlation with activation in the amgydala and caudate. In addition, there was a trend of positive correlation between feedback-related activation in the left lateral frontal cortex and subsequent increased risk-seeking behavior. These results suggest that a strong cognitive control mechanism but a weak affective decision-making and reinforcement learning mechanism that usually contribute to flexible, goal-directed decisions can lead to decision biases involving random events. This has significant implications for our understanding of the gambler's fallacy and human decision making under risk. Hum Brain Mapp, 2011. © 2010 Wiley-Liss, Inc.