Although major depression is projected to be among the top three causes of disability-adjusted life years lost in 2030, relatively little is known concerning the extent to which depressed mood states can bias social-economic decision making away from optimal outcomes. One experimental framework to study the interaction between negative emotion and social-economic decisions is the ultimatum game (UG), where the fair, cooperative player altruistically punishes the unfair, non-cooperative player. To assess a potential susceptibility of altruistic punishment to depressed mood, we repeatedly administered the UG task to a cohort of 20 currently depressed patients with a diagnosis of recurrent major depressive disorder and 20 healthy controls. Furthermore, valence and arousal ratings of emotionally laden pictures were obtained from all participants in order to assess a depressed mood-related distortion of emotion judgments. Compared to healthy controls, depressed patients over-sanctioned unfair proposals in the UG and judged emotional stimuli too negatively. Thus, major depression is associated with a negative emotional bias that hampers social-economic decision making and produces large personal costs.