Adolescence is characterized by increases in both perceived stress and risk-taking, although the effects of stress on risk-sensitive decision-making have received little attention in adolescent groups. We report psychophysiological data from the healthy control group of a larger project examining neuroendocrine and neuropsychological function in boys with conduct disorder. The present analysis focussed on healthy male adolescents (n = 66) performing a decision-making task that involved selection between two wheel-of-fortune gambles. The task was completed in a neutral state, and again following a psychosocial stress induction that robustly increased salivary cortisol levels and baseline autonomic arousal. Task-related changes in electrodermal activity (EDA) and heart rate (HR) were monitored during the receipt of win and loss outcomes. On gamble choice, stress attenuated the difference in risk taking between the losses-only and wins-only trials (the 'reflection effect') and reduced risk-taking on one further gamble type (i.e. a stress × gamble type interaction). In the neutral condition, EDA and HR deceleration responses were significantly greater for losses compared to wins. This physiological differentiation of losses and wins was reduced under stress, with a significant attenuation of the HR deceleration response. In addition, higher trait impulsivity scores predicted reduced EDA differentiation of the outcomes, and reduced EDA stress reactivity. As a limitation, the order of neutral and stress sessions was not counter-balanced. Reduced psychophysiological discrimination between positive and negative outcomes may contribute to the effects of stress on risky decision-making in adolescents.