In this study, we investigate the relationship between stress and flow-experience with the help of psychophysiological arousal indicators. Whereas recent studies suggest a positive relation between flow and physiological arousal, so far nothing is known on the relation between flow and high arousal in response to a salient stressor. We here suggest that the relation of flow with sympathetic arousal and hypothalamic–pituitary–adrenal (HPA) axis activation follows an inverted u-curve rather than a linear function: moderate physiological arousal should facilitate flow-experience, whereas excessive physiological arousal should hinder flow. In order to experimentally stimulate high physiological arousal, we exposed 22 healthy male participants to a modified version of the Trier Social Stress Test. Then, participants had to perform a complex computer task for 60 minutes and to rate their flow-experience on the Flow Short-Scale directly after task completion. During the experiment, cortisol samples were taken every 15 minutes, and heart rate variability measures were assessed by continuous electrocardiography. We found an inverted u-shaped relationship of flow-experience with indices of sympathetic arousal and cortisol, whereas parasympathetic indices of heart rate control during stress were linearly and positively correlated with flow-experience. Our results suggest that moderate sympathetic arousal and HPA-axis activation and possibly a co-activation of both branches of the autonomic nervous system characterize task-related flow-experience.