Reward processing permits to establish if and how an environmental stimulus or a future goal is reinforcing or punishing for the subject. This process is at the basis of reinforcement learning and decision making; is principally based on the orbitofrontal cortex and its connections with the striatum and the limbic system. If a dysfunctional reward processing has been often reported in substance abusers or pathologic gamblers, recent studies reported a dysfunction of this process in patients with other psychiatric disorders, previously not assessed by this experimental perspective, for example attention deficit/hyperactivity disorder, mood disorders, eating behaviour disorders and cluster B personality disorders. Experimental findings on a dysfunctional reward processing in these disorders are reviewed and discussed, in order to trace directions for future studies, that need to clarify if different dysfunctions are associated to different psychiatric disorders.