Obesity and weight gain are severe complications of mental illness, especially schizophrenia. They result from changes in lifestyle and nutrition, side effects of medication and other, less well-understood factors. Recent studies suggest that obesity and weight gain are linked to psychopathology. Specifically, severe psychopathology is associated with greater weight dysregulation, typically weight gain. However, our knowledge about the neuroscientific basis of weight gain in schizophrenia is currently limited. We propose that altered reward anticipation, which in turn is related to striatal dopaminergic dysregulation, may explain why obesity is more prevalent in individuals with mental illness. We review evidence that reward anticipation and weight change are linked by a core deficit in dopaminergic striatal circuits. Several lines of evidence, running from animal studies to preclinical and clinical studies, suggest that striatal dopaminergic neurotransmission is a major hub for the regulation of eating behavior and that dopamine links eating behavior to other motivated behavior. From this perspective, the present review outlines a unifying perspective on dopaminergic reward anticipation as a theoretical frame to link weight gain, medication effects and psychopathology. We derive important but open empirical questions and present perspectives for new therapeutic concepts.