Approximately half of the people with psychotic disorders from the schizophrenia group also develop a comorbid addictive disorder during their lifetime. These so-called dual diagnosis patients (DD) are difficult to treat. They have poor compliance and frequent relapses, they often present with aggressive behavior towards themselves and others and the long- term sociorehabilitative outcomes are poor. In this article the different models for the understanding of the high comorbidity between psychoses and substance use disorders are explained and the principles for an integrated treatment of DD patients are outlined. Low-threshold, motivational, integrated treatment programs with psychoeducative and behavioral therapeutic elements are helpful and should be more extensively implemented; however, long- term treatment methods are needed and therapeutic goals must be realistic and not set too high.