The dual diagnosis schizophrenia and addiction represents a combination of an endogenous psychosis and an addictive condition in the sense of abuse of or dependence on psychotropic substances. Before this diagnosis is established, schizophreniform organic psychoses must be distinguished from primary schizophrenia. Since the psychopathological differentiation is often not quite unequivocal, a search must be made for treatable underlying disorders. Here, help is afforded by the patient's history obtained on the basis of the reports of relatives and friends, physical neurologic examinations, and various laboratory, radiologic, electrophysiologic and neuropsychologic methods. In the daily clinical situation, a series of characteristic leading symptoms help clarify the differential diagnosis. The starting point for treatment is the patient's personal view of the problem, and his subjective state of health. Goals to be aimed at include integrative therapeutic approaches propagating the interaction of pharmacotherapy, psychotherapy and sociotherapy.