Two experiments are reported, which test the hypothesis that acute stress leads to suboptimal decisions under uncertainty (outcomes known but not their probabilities), due to a stressor caused bias toward the preference for positive feedbacks. The published literature suggests that acute stress leads to suboptimal decision-making, but only for those subjects who show a strong cortisol response. The stress hormone cortisol biases the reward system towards a preference for positive feedbacks, while ignoring or neglecting negative feedbacks. A critical review of the literature revealed, that this hypothesis has a questionable data basis. Additionally, there is not a single study using a direct cortical index of feedback processing. The Feedback Related Negativity (FRN), a component of the event-related potential, is measured as a direct index of optimal feedback processing. Both experiments used the Social Evaluated Cold Pressure Test (SECPT) as a stress paradigm. The Balloon Analogue Risk Task (BART) was decision-making procedure in experiment 1, whereas experiment 2 used the Iowa Gambling Task (IGT). The FRN was measured contingent on positive and negative feedbacks during the decision tasks. Three groups were analyzed: two SECPT groups (cortisol high vs cortisol low responders), and a control group performing the Social Evaluated Warm Pressure Test. Though all manipulation checks regarding the behavioral and biological results of the acute stressor and the BART or the IGT could be validated empirically, both experiments revealed no influence of the acute stressor on decision making under uncertainty or on feedback processing, as indexed by the FRN. It is concluded that acute stress has no negative influence on decision-making under uncertainty. Possible objections to this conclusion are discussed in the final sections of this thesis, before developing a basic paradigm, which might guide future research in this field.