The need to belong, a fundamental concept in psychology, organizes a wide range of findings in the study of interpersonal relationships. We suggest that human belongingness needs can be illuminated by examining when they go awry. We review research on social anhedonia, a trait that involves a marked disinterest in interpersonal contact. Social anhedonia has a long history in clinical psychology, particularly in the study of schizotypy and schizophrenia-spectrum disorders, but it is just starting to get attention from social and personality psychologists. Three lines of research—cross-sectional studies of individual differences, longitudinal studies of risk for psychopathology, and experience-sampling studies of interpersonal behavior—suggest that (1) social anhedonia represents genuine social disinterest, not merely shyness, introversion, or social anxiety, and (2) people high in social anhedonia have consistently poorer functioning, including a higher risk for developing schizophrenia-spectrum disorders. Just as satisfied relatedness needs promote flourishing, dysfunctional social needs promote psychopathology.