A central aspect of many psychiatric disorders is the disturbance of decision-making in social interactions. This disturbance importantly contributes to the severe social consequences of these conditions. The combination of economic game theory and neuroscience opens up the potential to examine dysfunctional social behavior at the computational level, including psychological, social and biological information in the same model. In current studies, we examine social decision-making in patients with depression, bipolar disorder, borderline personality disorder and autism spectrum disorder using simple social experiments. We found that social decision-making is less consistent in patients with borderline personality disorder than in depressed individuals, patients with autism and controls. Adult patients with autism spectrum disorders showed reduced unconditional altruism in our experiments. Patients with major depressive disorder specifically exhibited competition avoidance. We currently examine the neural substrate of abnormal social decision-making using fMRI.